Scientific American Supplement, No. 303, October 22, 1881

Chapter 7

Chapter 73,597 wordsPublic domain

_Note on annealing glass tubes._--It is quite necessary to anneal all those parts of the pump that are to be exposed to heat, otherwise they soon crack. I found by inclosing the glass in heavy iron tubes and exposing it for five hours to a temperature somewhat above that of melting zinc, and then allowing an hour or two for the cooling process, that the strong polarization figure which it displays in a polariscope was completely removed, and hence the glass annealed. A common gas-combustion furnace was used, the bends, etc, being suitably inclosed in heavy metal and heated over a common ten-fold Bunsen burner. Thus far no accident has happened to the annealed glass, even when cold drops of mercury struck in rapid succession on portions heated considerably above 100° C.

I wish, in conclusion, to express my thanks to my assistant, Dr. Ihlseng, for the labor he has expended in making the large number of computations necessarily involved in work of this kind.--_Amer. Jour. of Science._

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CRYSTALLIZATION TABLE.

The following table, prepared by E. Finot and Arm. Bertrand for the _Jour. de Ph. et de Chim._, shows the point at which the evaporation of certain solutions is to be interrupted in order to procure a good crop of crystals on cooling. The density is according to Baumé's scale, the solution warm:

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THE PRINCIPLES OF HOP-ANALYSIS.

By Dr. G. O. CECH

[Footnote: 'Zeitschrift fur Analyt. Chemie,' 1881.]

Hop flowers contain a great variety of different substances susceptible of extraction with ether, alcohol, and water, and distinguishable from one another by tests of a more or less complex character. The substances are: Ethereal oil, chlorophyl, hop tannin, phlobaphen, a wax-like substance, the sulphate, ammoniate, phosphate, citrate and malates of potash, arabine, a crystallized white and an amorphous brown resin, and a bitter principle. That the characteristic action of the hops is due to such of these constituents only as are of an organic nature is easy to understand; but up to the present we are in ignorance whether it is upon the oil, the wax, the resin, the tannin, the phlobaphen, or the bitter principle individually, or upon them all collectively, that the effect of the hops in brewing depends.

It is the rule to judge the strength and goodness of hops by the amount of farina--the so-called lupuline; and as this contains the major portion of the active constituents of the hop, there is no doubt that approximately the amount of lupuline is a useful quantitative test. But here we are confronted by the question whether the lupuline is to be regarded as containing _all_ that is of any value in the hops and the leaves, the organic principles in which pass undetected under such a test, as supererogatory for brewers' purposes? Practical experience negatives any such conclusion. Consequently, we are justified in assuming that the concurrent development and the presence of the several organic principles--the oil, the wax, the bitter, the tannin, the phlobaphen, in the choicer sorts--are subject, within certain limits, to variations depending on skilled culture and careful drying, and that the aggregate of these principles has a certain attainable maximum in the finer sorts, under the most favorable conditions of culture, and another, lower maximum in less perfectly cultivated and wild sorts. The difference in the proportion of active organic substance in each sort must be determined by analysis. There then remains to be discovered which of the aforesaid substances plays the leading role in brewing, and also whether the presence of chlorophyl and inorganic salts in the hop extract influences or alters the results.

That in brewing hops cannot be replaced by lupuline alone, even when the latter is employed in relatively large quantities is well known, as also that a considerable portion of the bitter principle of the hop is found in the floral leaves. Neither can the lupuline be regarded as the only active beer agent, as both the hop-tannin and the hop-resin serve to precipitate the albuminous matter, and clarify and preserve the beer.

Both chemists and brewers would gladly welcome some method of testing hops, which should be expeditious, and afford reliable results in practical hands. To accomplish this account must be taken of all the active organic constituents of the hops, which can be extracted either with ether, alcohol, or water containing soda (for the conversion of the hop tannin in phlobaphen).[1] It should further be ascertained whether the chlorophyl percentage in the hop bells, new and old, is or is not the same in cultivated and in wild hops, and whether the aggregate percentages of organic and constituent observe the same limits.

[Footnote 1: See C. Etti, in "Dingler's Polytech. Journ.," 1878, p. 354.]

As wild hops nowadays are frequently introduced in brewing, the proportion of chlorophyl and organic and inorganic constituents in them should be compared with those of cultivated sorts, taking the best Bavarian or Bohemian hops as the standard of measurement. The chlorophyl is of minor importance, as it has little effect on the general results.

By a series of comparative analysis of cultivated and wild hops, in which I would lay especial stress on parity of conditions in regard of age and vegetation, the extreme limits of variation of which their active organic principles are susceptible could be determined.

There is every reason to suppose that the chlorophyl and inorganic constituents do not differ materially in the most widely different sorts of hops. The more important differences lie in the proportions of hop resin and tannin. When this is decided, the proportion of tannin or phlobaphen in the hop extract or the beer can be determined by analysis in the ordinary way. But whenever some quick and sure hop test shall have been found, _appearance and aroma_ will still be most important factors in any estimate of the value of hops. Here a question arises as to whether hops from a warm or even a steppe climate, like that of South Russia, contain the same proportion of ethereal oil--that is, of aroma--as those from a cooler climate, like Bavaria and Bohemia, or like certain other fruit species of southern growth, they are early in maturing, prolific, large in size, and abounding in farina, but _deficient in aroma_.

The bearings of certain experimental data on this point I reserve for consideration upon a future occasion.--_The Analyst_.

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WATER GAS.

A DESCRIPTION OF APPARATUS FOR PRODUCING CHEAP GAS, AND SOME NOTES ON THE ECONOMICAL EFFECT OF USING SUCH GAS WITH GAS MOTORS, ETC.

[Footnote: Abstract of paper read in Section G. British Association, York]

By MR. J. EMERSON DOWSON, C.E., of London.

In many countries and for many years past, inventors have sought some cheap and easy means of decomposing steam in the presence of incandescent carbon in order to produce a cheap heating gas; and working with the same object the writer has devised an apparatus which has been fitted up in the garden of the Industrial Exhibition, and is there making gas for a 3½ horse power (nominal) Otto gas engine. The retort or generator consists of a vertical cylindrical iron casing which incloses a thick lining of ganister to prevent loss of heat and oxidation of the metal, and at the bottom of this cylinder is a grate on which a fire is built up. Under the grate is a closed chamber, and a jet of superheated steam plays into this and carries with it by induction a continuous current of air. The pressure of the steam forces the mixture of steam and air upward through the fire, so that the combustion of the fuel is maintained while a continuous current of steam is decomposed, and in this way the working of the generator is constant, and the gas is produced without fluctuations in quality. The well-known reactions occur, the steam is decomposed, and the oxygen from the steam and air combines with the carbon of the fuel to form carbon dioxide (CO_2), which is reduced to the monoxide (CO) on ascending the fuel column. In this way the resulting gases form a mixture of hydrogen, carbon, monoxide, and nitrogen, with a small percentage of carbon dioxide which usually escapes without reduction. The steam should have a pressure of 1½ to 2 atmospheres, and is produced and superheated in a zigzag coil fed with water from a neighboring boiler. The quantity of water required is very small, being only about 7 pints for each 1,000 cubic feet of gas, and, except on the first occasion when the apparatus is started, the coil is heated by some of the gas drawn from the holder, so that after the gas is lighted under the coil the superheater requires no attention.

For boiler and furnace work the gas can be used direct from the generator; but where uniformity of pressure is essential, as for gas engines, gas burners, etc., the gas should pass into a holder. The latter somewhat retards the production, but the steam injector causes gas to be made so rapidly that a holder is easily filled against a back pressure of 1 in. to 1½ in. of water, and at this pressure the generator can pass gas continuously into the holder, while at the same time it is being drawn off for consumption.

The nature of the fuel required depends on the purpose for which the gas is used. If for heating boilers, furnaces, etc, coke or any kind of coal maybe used; but for gas engines or any application of the gas requiring great cleanliness and freedom from sulphur and ammonia it is best to use anthracite, as this does not yield condensable vapors, and is very free from impurities. Good qualities of this fuel contain over 90 per cent of carbon and so little sulphur that, for some purposes, purification is not necessary. For gas engines, etc., it is, however, better to pass the gas through some hydrated oxide of iron to remove the sulphureted hydrogen. The oxide can be used over and over again after exposure to the air, and the purifying is thus effected without smell or appreciable expense. Gas made by this process and with anthracite coal has no tar and no ammonia, and the small percentage of carbon dioxide present does not sensibly affect the heating power. A further advantage of this gas is that it cannot burn with a smoky flame, and there is no deposition of soot even when the object to be heated is placed over or in the flame, and this is of importance for the cylinder and valves of a gas engine.

To produce 1,000 cubic feet only 12 lb. of anthracite are required, allowing 8 to 10 per cent, for impurities and waste; thus a generator A size, which produces 1,000 cubic feet per hour, needs only 12 lb. in that time, and this can be added once an hour or at longer intervals. No skilled labor is necessary, and in practice it is usual to employ a man who has other work to attend to near the generator, and to pay him a small addition to his usual wages.

The comparative explosive force of coal gas and the Dowson gas calculated in the usual way is as 3.4:1, i. e., coal gas has 3.4 times more energy than the writer's gas. Messrs. Crossley, of Manchester, the makers of the Otto gas engines, have made several careful trials of this gas with some of their 3½ horse power (nominal) engines, and in one trial they took diagrams every half-hour for nine consecutive days. These practical trials have shown that without altering the cylinder of the engine it is possible to admit enough of the Dowson gas to give the same power as with ordinary coal gas. It has been seen that the comparative explosive force of the two gases is as 3.4:1, but as it is well known the combustion of carbon monoxide proceeds at a comparatively slow rate, and for this reason, and because of the diluents present in the cylinder which affect the weaker gas more than coal gas, experience has shown that it is best to allow five volumes of the Dowson gas for one volume of coal gas, and then the same uniform power is obtained as with the latter.

This gives very important economical results; for if the cost of the Dowson gas given in the tables as 4¼d., 3-1/3d., and 2¾d. per 1,000 cubic feet, be multiplied by 5 there will be 1s. 9¼d., 1s. 4¾d., and 1s. 2¾d., or a mean of 1s. 5½d. for the equivalent of 1,000 cubic feet of coal gas, which usually costs from 3s. to 4s., and this represents an actual saving of about 50 to 60 per cent, in working cost. Another practical consideration is that coal gas requires 224 lb. to 250 lb. of coal per 1,000 cubic feet of gas, but the writer requires only 12 lb. per 1,000 cubic feet, and multiplying this by 5 to give the equivalent of 1,000 cubic feet of coal gas, for engine work, there are 60 lb. instead of 224 lb. to 250 lb. This is only 24 to 27 per cent, of the weight of the coal required for coal gas, and in many outlying districts this will effect an appreciable saving in the cost of transport.

APPENDIX.

TABLE I.

_Generator A Size_ (producing 1,000 cubic feet per hour): Anthracite to make gas at the rate of 1,000 s. d. cubic feet per hour=l2 lb x 9 working hours=l08 lb., or say, 1 cwt. at 20s. a ton.................................... 1 0 Allowance for wages of attendant......... 1 0 Repairs and depreciation of generator, gasholder, etc. (5 per cent. on £l25)= per working day........................ 0 5 Interest on capital outlay, ditto........ 0 5 ______

Total........................... 2 10 cub. ft.

Gas produced............................. 9.000 Less gas used for generating and superheating steam..................... 1,000 _____ Total effective gas for 2s. 10d. 8,000

Net cost 4¼ d. per 1,000 cubic feet.

TABLE II.

_Generator B Size_ (producing 1,500 cubic feet per hour) Anthracite to make gas at the rate of 1,500 s. d. cubic feet per hour=18 lb. x 9 working hours=162 lb., or, say, 1½ cwt. 20s. a ton.................................. 1 6 Allowance for wages of attendant......... 1 0 Repairs and depreciation of generator, gasholder, etc. (5 per cent, on £140) =per working day....................... 0 5½ Interest on capital outlay, ditto........ 0 5½ ___ ___ Total........................... 3 5 cub. ft. Gas produced............................. 13,500 Less gas used for generating and superheating steam..................... 1,200 ______ Total effective gas for 3s. 5d.. 12,300

Net cost 3 1/3d. per 1,000 cubic feet.

TABLE III.

_Generator C Size_ (producing 2,500 cubic feet per hour): Anthracite to make gas at the rate of 2,500 s. d. cubic feet per hour=30 lb. x 9 working hours=270 lb. at 20s. a ton............ 2 4½ Allowance for wages of attendant....... 1 6 Repairs and depreciation of generator, gasholder, etc. (5 per cent, on £160)= per working day...................... 0 6½ Interest on capital outlay, ditto...... 0 6½ _______ Total......................... 4 11½

cub. ft. Gas produced........................... 22,500 Less gas used for generating and superheating steam................... 1,500 ______ Total effective gas for 4s. 11½d 21,000

Net cost, say, 2¾ d. per 1,000 cubic feet.

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ON THE FLUID DENSITY OF CERTAIN METALS.

[Footnote: Abstract of paper read before Section C (Chemical Science), British Association meeting, York.]

By PROFESSOR W. CHANDLER ROBERTS, F.R.S., and T. WRIGHTSON.

The authors described their experiments on the fluid density of metals made in continuation of those submitted to Section B at the Swansea meeting of the Association. Some time since one of the authors gave an account of the results of experiments made to determine the density of metallic silver, and of certain alloys of silver and copper when in a molten state. The method adopted was that devised by Mr. R. Mallet, and the details were as follows: A conical vessel of best thin Lowmoor plate (1 millimeter thick), about 16 centimeters in height, and having an internal volume of about 540 cubic centimeters, was weighed, first empty, and subsequently when filled with distilled water at a known temperature. The necessary data were thus afforded for accurately determining its capacity at the temperature of the air. Molten silver was then poured into it, the temperature at the time of pouring being ascertained by the calorimetric method. The precautions, as regards filling, pointed out by Mr. Mallet, were adopted; and as soon as the metal was quite cold, the cone with its contents was again weighed. Experiments were also made on the density of fluid bismuth; and two distinctive determinations gave the following results:

10.005 ) ) mean 10.039. 10.072 )

The invention of the oncosimeter, which was described by one of the authors in the "Journal of the Iron and Steel Institute" (No. II., 1879, p. 418), appeared to afford an opportunity for resuming the investigation on a new basis, more especially as the delicacy of the instrument had already been proved by experiments on a considerable scale for determining the density of fluid cast iron. The following is the principle on which this instrument acts:

If a spherical ball of any metal be plunged below the surface of a molten bath of the same or another metal, the cold ball will displace its own volume of molten metal. If the densities of the cold and molten metal be the same, there will be equilibrium, and no floating or sinking effect will be exhibited. If the density of the cold be greater than that of the molten metal, there will be a sinking effect, and if less a floating effect when first immersed. As the temperature of the submerged ball rises, the volume of the displaced liquid will increase or decrease according as the ball expands or contracts. In order to register these changes the ball is hung on a spiral spring, and the slightest change in buoyancy causes an elongation or contraction of this spring which can be read off on a scale of ounces, and is recorded by a pencil on a revolving drum. A diagram is thus traced out, the ordinates of which represent increments of volume, or, in other words, of weight of fluid displaced--the zero line, or line corresponding to a ball in a liquid of equal density, being previously traced out by revolving the drum without attaching the ball of metal itself to the spring, but with all other auxiliary attachments. By means of a simple adjustment the ball is kept constantly depressed to the same extent below the surface of the liquid; and the ordinate of this pencil line, measuring from the line of equilibrium, thus gives an exact measure of the floating or sinking effect at every stage of temperature, from the cold solid to the state when the ball begins to melt.

If the weight and specific gravity of the ball be taken when cold, there are obtained, with the ordinate on the diagram at the moment of immersion, sufficient data for determining the density of the fluid metal; for

W / W1 = D / D1

the volumes being equal. And remembering that

W (weight of liquid) = W1 (weight of ball) + x

(where x is always measured as +_ve_ or -_ve_ floating effect), there is obtained the equation:

D1 x ( W1 + x) D = --------------- . W1

[TEX: D = \frac{D_1 \times (W_1 +x)}{W_1}]

The results obtained with metallic silver are perhaps the most interesting, mainly from the fact that the metal melts at a higher temperature, which was determined with great care by the illustrious physicist and metallurgist, the late Henri St. Claire Deville, whose latest experiments led him to fix the melting point at 940° Cent. The authors of the paper showed that the density of the fluid metal was 9.51 as compared with 10.57, the density of the solid metal. Taking their results generally, it is found that the change of volume of the following metals in passing from the solid to the liquid state may be thus stated:

Specific Specific Metal. Gravity, Gravity, Percentage of Solid. Liquid. Change.