Chapter 2

I may now say a few words on the defects and failures sometimes met with in working this process; and first in regard to the yellowing of the whites. I hear frequent complaints of this want of purity in the whites, especially in vignetted enlargements, and I believe that this almost always arises from one or other of the two following causes:

First. An excess of the ferrous salt in the ferrous oxalate developer; and when this is the case, the yellow compound salt is more in suspension than solution, and in the course of development it is deposited upon, and at the same time formed in, the gelatinous film.

The proportions of saturated solution of oxalate to saturated solution of iron, to form the oxalate of iron developer, that has been recommended by the highest and almost only scientific authority on the subject--Dr. Eder--are from 4 to 6 parts of potassic oxalate to 1 part of ferrous sulphate.

Now while these proportions may be the best for the development of a negative, they are not, according to my experience, the best for gelatine bromide positive enlargements; I find, indeed, that potassic oxalate should not have more than one-eighth of the ferrous sulphate solution added to it, otherwise it will not hold in proper solution for any length of time the compound salt formed when the two are mixed.

The other cause is the fixing bath. This, for opals and vignetted enlargements especially, should always be fresh and pretty strong, so that the picture will clear rapidly before any deposit has time to take place, as it will be observed that very shortly after even one iron developed print has been fixed in it a deposit of some kind begins to take place, so that although it may be used a number of times for fixing prints that are meant to be colored afterward it is best to take a small quantity of fresh hypo for every enlargement meant to be finished in black and white. The proportions I use are 8 ounces to the pint of water. Almost the only other complaints I now hear are traceable to over-exposure or lack of intelligent cleanliness in the handling of the paper. The operator, after having been dabbling for some time in hypo, or pyro, or silver solution, gives his hands a wipe on the focusing cloth, and straightway sets about making an enlargement, ending up by blessing the manufacturer who sent him paper full of black stains and smears. Argentic paper is capable of yielding excellent enlargements, but it must be intelligently exposed, intelligently developed, and cleanly and carefully handled.

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THE MANUFACTURE AND CHARACTERISTICS OF PHOTOGRAPHIC LENSES.

At a recent meeting of the London and Provincial Photographic Association Mr. J. Traill Taylor, formerly of New York, commenced his lecture by referring to the functions of lenses, and by describing the method by which the necessary curves were computed in order to obtain a definite focal length. The varieties of optical glass were next discussed, and specimens (both in the rough and partly shaped state) were handed round for examination. The defects frequently met with in glass, such as striæ and tears, were then treated upon; specimens of lenses defective from this cause were submitted to inspection, and the mode of searching for such flaws described. Tools for grinding and polishing lenses of various curvatures were exhibited, together with a collection of glass disks obtained from the factory of Messrs. Ross & Co., and in various stages of manufacture--from the first rough slab to the surface of highest polish. Details of polishing and edging were gone into, and a series of the various grades of emery used in the processes was shown. The lecturer then, by means of diagrams which he placed upon the blackboard, showed the forms of various makes of photographic lenses, and explained the influence of particular constructions in producing certain results; positive and negative spherical aberration, and the manner in which they are made to balance each other, was also described by the aid of diagrams, as was also chromatic aberration. He next spoke of the question of optical center of lenses, and said that that was not, as had been hitherto generally supposed, the true place from which to measure the focus of a lens or combination. This place was a point very near the optical center, and was known as the "Gauss" point, from the name of the eminent German mathematician who had investigated and made known its properties, the knowledge of which was of the greatest importance in the construction of lenses. A diagram was drawn to show the manner of ascertaining the two Gauss points of a bi-convex lens, and a sheet exhibited in which the various kinds of lenses with their optical centers and Gauss points were shown. For this drawing he (Mr. Taylor) said he was indebted to Dr. Hugo Schroeder, now with the firm of Ross & Co. The lecturer congratulated the newly-proposed member of the Society, Mr. John Stuart, for his enterprise in securing for this country a man of such profound acquirements. The subject of distortion was next treated of, and the manner in which the idea of a non distorting doublet could be evolved from a single bi-convex lens by division into two plano-convex lenses with a central diaphragm was shown. The influence of density of glass was illustrated by a description of the doublet of Steinheil, the parent of the large family of rapid doublets now known under various names. The effect of thickness of lenses was shown by a diagram of the ingenious method of Mr. F. Wenham, who had long ago by this means corrected spherical aberration in microscopic objective. The construction of portrait lenses was next gone into, the influence of the negative element of the back lens being especially noted. A method was then referred to of making a rapid portrait lens cover a very large angle by pivoting at its optical center and traversing the plate in the manner of the pantoscopic camera. The lecturer concluded by requesting a careful examination of the valuable exhibits upon the table, kindly lent for the occasion by Messrs. Ross & Co.

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IMPROVED DEVELOPERS FOR GELATINE PLATES.

By Dr. Eder.

We are indebted to Chas. Ehrmann, Esq., for the improved formulas given below as translated by him for the _Photographic Times_.

Dr. Eder has for a considerable time directed especial attention to the soda and potash developers, either of which seems to offer certain advantages over the ammoniacal pyrogallol. This advantage becomes particularly apparent with emulsions prepared with ammonia, which frequently show with ammoniacal developer green or red fog, or a fog of clayish color by reflected, and of pale purple by transmitted light. Ferrous oxalate works quite well with plates of that kind; so do soda and potassa developers.

For soda developers, Eder uses a solution of 10 parts of pure crystallized soda in 100 parts of water. For use, 100 c.c. of this solution are mixed with 6 c.c. of a pyrogallic solution of 1:10, without the addition of any bromide.

More pleasant to work with is Dr. Stolze's potassa developer. No. 1: Water, 200 c.c.; chem. pure potassium carbonate, 90 gr.; sodium sulphite, 25 gr. No. 2: Water 100 c.c.; citric, 1½ gr.; sodium sulphite, 25 gr.; pyrogallol., 12 gr. Solution No. 2 is for its better keeping qualities preferable to Dr. Stolze's solution.[A] The solutions when in well stoppered bottles keep well for some time. To develop, mix 100 c.c. of water with 40 min. of No. 1 and 50 min. of No. 2. The picture appears quickly and more vigorously than with iron oxalate. If it is desirable to decrease the density of the negatives, double the quantity of water. The negatives have a greenish brown to olive-green tone. A very fine grayish-black can be obtained by using a strong alum bath between developing and fixing. The same bath after fixing does not act as effectual in producing the desired tone. A bath of equal volumes of saturated solutions of alum and ferrous sulphate gives the negative a deep olive-brown color and an extraordinary intensity, which excludes all possible necessities of an after intensification.

[Footnote A: 100 c.c. water; 10 c.c. alcohol; 10 gr. pyrogallol; 1 gr. salicylic acid.]

The sensitiveness with this developer is at least equal to that when iron developer is used, frequently even greater.

The addition of bromides is superfluous, sometimes injurious. Bromides in quantities, as added to ammoniacal pyro, would reduce the sensitiveness to 1/10 or 1/20; will even retard the developing power almost entirely.

Must a restrainer be resorted to, 1 to 3 min. of a 1:10 solution of potassium bromide is quite sufficient.

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THE PREPARATION OF LARD FOR USE IN PHARMACY.

[Footnote: Read at an evening meeting of the Pharmaceutical Society of Great Britain, November 7, 1883.]

By Professor REDWOOD.

I have read with much, interest the paper on "Ointment Bases," communicated by Mr. Willmott to the Pharmaceutical Conference at its recent meeting, but the part of the subject which has more particularly attracted my attention is that which relates to prepared lard. Reference is made by Mr. Willmott to lard prepared in different ways, and it appears from the results of his experiments that when made according to the process of the British Pharmacopoeia it does not keep free from rancidity for so long a time as some of the samples do which have been otherwise prepared. The general tendency of the discussion, as far as related to this part of the subject, seems to have been also in the same direction; but neither in the paper nor in the discussion was the question of the best mode of preparing lard for use in pharmacy so specially referred to or fully discussed as I think it deserves to be.

When, in 1860, Mr. Hills, at a meeting of the Pharmaceutical Society, suggested a process for the preparation of lard, which consisted in removing from the "flare" all matter soluble in water, by first thoroughly washing it in a stream of cold water after breaking up the tissues and afterward melting and straining the fat at a moderate heat, this method of operating seemed to be generally approved. It was adopted by men largely engaged in "rendering" fatty substances for use in pharmacy and for other purposes for which the fat was required to be as free as possible from flavor and not unduly subject to become rancid. It became the process of the British Pharmacopoeia in 1868. In 1869 it formed the basis of a process, which was patented in Paris and this country by Hippolite Mege, for the production of a fat free from taste and odor, and suitable for dietetic use as a substitute for butter. Mege's process consists in passing the fat between revolving rollers, together with a stream of water, and then melting at "animal heat." This process has been used abroad in the production of the fatty substance called oleomargarine.

But while there have been advocates for this process, of whom I have been one, opinions have been now and then expressed to the effect that the washing of the flare before melting the fat was rather hurtful than beneficial. I have reason to believe that this opinion has been gaining ground among those who have carefully inquired into the properties of the products obtained by the various methods which have been suggested for obtaining animal fat in its greatest state of purity.

I have had occasion during the last two or three years to make many experiments on the rendering and purification of animal fat, and at the same time have been brought into communication with manufacturers of oleomargarine on the large scale; the result of which experience has been that I have lost faith in the efficacy of the Pharmacopeia process. I have found that in the method now generally adopted by manufacturers of oleomargarine, which is produced in immense quantities, the use of water, for washing the fat before melting it, is not only omitted but specially avoided. The parts of the process to which most importance is attached are: First, the selection of fresh and perfectly sweet natural fat, which is hung up and freely exposed to air and light. It thus becomes dried and freed from an odor which is present in the freshly slaughtered carcass. It is then carefully examined, and adhering portions of flesh or membrane as far as possible removed; after which it is cut up and passed through a machine in which it is mashed so as to completely break up the membraneous vesicles in which the fat is inclosed. The magma thus produced is put into a deep jacketed pan heated by warm water, and the fat is melted at a temperature not exceeding 130°F.

If the flare has been very effectually mashed, the fat may be easily melted away from the membraneous matter at 120°F., or even below that, and no further continuance of the heat is required beyond what is necessary for effecting a separation of the melted fat from the membraneous or other suspended matter. Complete separation of all suspended matter is obviously important, and therefore nitration seems desirable, where practicable; which however is not on the large scale.

My experiments tend to indicate that the process just described is that best adapted for the preparation of lard for use in pharmacy. There is, however, a point connected with this or any other method of preparing lard which is deserving of more attention than it has, I believe, usually received, and that is, the source from which the flare has been derived. Everybody knows how greatly the quality of pork depends upon the manner in which the pig has been fed, and this applies to the fat as well as other parts of the animal. Some time ago I had some pork submitted to me for the expression of opinion upon it, which had a decided fishy flavor, both in taste and smell. This flavor was present in every part, fat and lean, and it is obvious that lard prepared from that fat would not be fit for use in pharmacy. The pig had been prescribed a fish diet. Barley meal would, no doubt, have produced a better variety of lard.

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ANTI-CORROSION PAINT.

The _Neueste Erfinderung_ describes an anti-corrosion paint for iron. It states that if 10 per cent. of burnt magnesia, or even baryta, or strontia, is mixed (cold) with ordinary linseed-oil paint, and then enough mineral oil to envelop the alkaline earth, the free acid of the paint will be neutralized, while the iron will be protected by the permanent alkaline action of the paint. Iron to be buried in damp earth may be painted with a mixture of 100 parts of resin (colophony), 25 parts of gutta-percha, and 50 parts of paraffin, to which 20 parts of magnesia and some mineral oil have been added.

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CARBON IN STEEL.

At a recent meeting of the Chemical Society, London, a paper was read entitled "Notes on the Condition in which Carbon exists in Steel," by Sir F.A. Abel, C.B., and W.H. Deering.

Two series of experiments were made. In the first series disks of steel 2.5 inches in diameter and 0.01 inch thick were employed. They were all cut from the same strip of metal, but some were "cold-rolled," some "annealed," and some "hardened." The total carbon was found to be: "cold-rolled," 1.108 per cent.; hardened, 1.128 per cent.; and annealed, 0.924 and 0.860 per cent. Some of the disks were submitted to the action of an oxidizing solution consisting of a cold saturated solution of potassium bichromate with 5 per cent. by volume of pure concentrated sulphuric acid. In all cases a blackish magnetic residue was left undissolved. These residues, calculated upon 100 parts of the disks employed, had the following compositions: "Cold-rolled" carbon, 1.039 per cent.; iron, 5.871. Annealed, C, 0.83 per cent.; Fe, 4.74 per cent. Hardened, C, 0.178 per cent.; Fe, 0.70 per cent. So that by treatment with chromic acid in the cold nearly the whole of the carbon remains undissolved with the cold-rolled and annealed disks, but only about one-sixth of the total carbon is left undissolved in the case of the hardened disk. The authors then give a _resume_ of previous work on the subject. In the second part they have investigated the action of bichromate solutions of various strengths on thin sheet-steel, about 0.098 inch thick, which was cold-rolled and contained: Carbon, 1.144 per cent.; silica, 0.166 per cent.; manganese, 0.104 per cent. Four solutions were used. The first contained about 10 per cent. of bichromate and 9 per cent. of H_{2}SO_{4} by weight; the second was eight-tenths as strong, the third about half as strong, the fourth about one and a half times as strong. In all cases the amount of solution employed was considerably in excess of the amount required to dissolve the steel used. A residue was obtained as before. With solution 1, the residue contained, C, 1.021; sol. 2, C, 0.969; sol. 3, C 1.049 the atomic ratio of iron to carbon was Fe 2.694: C, 1; Fe, 2.65: C, 1; Fe), 2.867 C, 1): sol. 4. C, 0.266 per 100 of steel. The authors conclude that the carbon in cold rolled steel exists not simply diffused mechanically through the mass of steel but in the form of an iron carbide, Fe_{3}C, a definite product, capable of resisting the action of an oxidizing solution (if the latter is not too strong), which exerts a rapid solvent action upon the iron through which the carbide is distributed.

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APPARATUS FOR EXTRACTING STARCH FROM POTATOES.

In the apparatus of Mr. Angele, of Berlin, shown in the annexed cuts (Figs. 1 and 2), the potatoes, after being cleaned in the washer, C, slide through the chute, v, into a rasp, D, which reduces them to a fine pulp under the action of a continuous current of water led in by the pipe, d. The liquid pulp flows into the iron reservoir, B, from whence a pump, P, forces it through the pipe, w, to a sieve, g, which is suspended by four bars and has a backward and forward motion. By means of a rose, c, water is sprinkled over the entire surface of the sieve and separates the fecula from the fibrous matter. The water, charged with fine particles of fecula, and forming a sort of milk, flows through the tube, z, into the lower part, N, of the washing apparatus, F, while the pulp runs over the sieve and falls into the grinding-mill, H. This latter divides all those cellular portions of the fecula that have not been opened by the rasp, and allows them to run, through the tube, h, into the washing apparatus, F, where the fecula is completely separated from woody fibers. The fluid pulp is carried by means of a helix, i, to a revolving perforated drum at e. From this, the milky starch flows into the jacket, N, while the pulp (ligneous fibers) makes its exit from the apparatus through the aperture, n, and falls into the reservoir, o.

The liquid from the jacket, N, passes to a refining sieve, K, which, like the one before mentioned, has a backward and forward motion, and which is covered with very fine silk gauze in order to separate the very finest impurities from the milky starch. The refined liquid then flows into the reservoir, m, and the impure mass of sediment runs into the pulp-reservoir, o. The pump, l, forces the milky liquid from the reservoir, m, to the settling back, while the pulp is forced by a pump, u, from the receptacle, o, into a large pulp-reservoir.

The water necessary for the manufacture is forced by the pump, a, into the reservoir, W, from whence it flows, through the pipes, r, into the different machines. All the apparatus are set in motion by two shaftings, q. The principal shaft makes two hundred revolutions per minute, but the velocity of that of the pumps is but fifty revolutions.--_Polytech. Journ., and Bull. Musee de l'Indust_.

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A SIMPLE APPARATUS FOR DESCRIBING ELLIPSES.

By Prof. E.J. HALLOCK.

A very simple apparatus for describing an oval or ellipse may be constructed by any apprentice or school boy as follows: Procure a straight piece of wood about ¼ inch wide by 1/8 inch thick and 13 inches long. Beginning ½ inch from the end, bore a row of small holes only large enough for a darning needle to pass through and half an inch apart. Mark the first one (at A) 0, the third 1, the fifth 2, and so on to 12, so that the numbers represent the distance from O in inches. A small slit may be made in the end of the ruler or strip of wood near A, but a better plan is to attach a small clip on one side.

Next procure a strong piece of linen thread about four feet long; pass it through the eye of a coarse needle, wax and twist it until it forms a single cord. Pass the needle _upward_ through the hole marked 0, and tie a knot in the end of the thread to prevent its slipping through. The apparatus is now ready for immediate use. It only remains to set it to the size of the oval desired.

Suppose it is required to describe an ellipse the longer diameter of which is 8 inches, and the distance between the foci 5 inches. Insert a pin or small tack loosely in the hole between 6 and 7, which is distant 6-½ inches from O. Pass the needle through hole 5, allowing the thread to pass around the tack or pin; draw it tightly and fasten it in the slit or clip at the end. Lay the apparatus on a smooth sheet of paper, place the point of a pencil at E, and keeping the string tight pass it around and describe the curve, just in the same manner as when the two ends of the string are fastened to the paper at the foci. The chief advantage claimed over the usual method is that it may be applied to metal and stone, where it is difficult to attach a string. On drawings it avoids the necessity of perforating the paper with pins.

As the pencil point is liable to slip out of the loop formed by the string, it should have a nick cut or filed in one side, like a crochet needle.

As the mechanic frequently wants to make an oval having a given width and length, but does not know what the distance between the foci must be to produce this effect, a few directions on this point may be useful:

It is a fact well known to mathematicians that if the distance between the foci and the shorter diameter of an ellipse be made the sides of a right angled triangle, its hypothenuse will equal the greater diameter. Hence in order to find the distance between the foci, when the length and width of the ellipse are known, these two are squared and the lesser square subtracted from the greater, when the square root of the difference will be the quantity sought. For example, if it be required to describe an ellipse that shall have a length of 5 inches and a width of 3 inches, the distance between the foci will be found as follows:

(5 x 5) - (3 x 3) = (4 x 4) or __ 25 - 9 = 16 and \/16 = 4.

In the shop this distance may be found experimentally by laying a foot rule on a square so that one end of the former will touch the figure marking the lesser diameter on the latter, and then bringing the figure on the rule that represents the greater diameter to the edge of the square; the figure on the square at this point is the distance sought. Unfortunately they rarely represent whole numbers. We present herewith a table giving the width to the eighth of an inch for several different ovals when the length and distance between foci are given.

Length. Distance between foci. Width. Inches. Inches. Inches.

2 1 1¾ 2 1½ 1¼

2½ 1 2¼ 2½ 1½ 2 2½ 2 1½

3 1 1½ 3 1½ 2-7/8 3 2 2-5/8 3 2½ 2¼