Chapter 7

Hermann W. Vogel has made a comparative study of the properties of silver bromide, obtained by precipitation in an aqueous solution of gelatin, and those of the same compound prepared by precipitation in an alcoholic solution of collodion. In 1874 Stas called attention to six modifications of silver bromide. One of these, granular bromide of silver, obtained by boiling the flocculent precipitate for several days with water, he stated, was the most sensitive to light of all substances known; exposure for two or three seconds to the pale blue flame of a Bunsen burner being sufficient to blacken it. Important as this fact was for photographers it was not applied for years, and it was only in 1878, when, it having been found that silver bromide precipitated in a gelatine solution and boiled for several hours becomes much more sensitive to light, that the remarks of Stas was recalled. Today these observations have become of the greatest importance to practical photography. They have led to the preparation of the silver bromide gelatin emulsion and the silver bromide gelatin plates, which are twenty times more sensitive than the silver iodide collodion plates, and have become indispensable when impressions are to be taken in a dim light.

The extraordinary sensitiveness of silver bromide in gelatin seemed the more remarkable since it was known that silver bromide in collodion is only moderately sensitive. The explanation was sought for in various directions, but as the result of numerous investigations it appears that the chief cause of the difference is the presence of different modifications of silver bromide. From a consideration of the work already done on the subject, Vogel suspected that silver bromide precipitated in an aqueous colloidal liquid would have notably different properties from silver bromide precipitated in an alcoholic colloidal solution. Silver bromide was prepared in many different ways. Emulsions were made in bromide solutions containing gelatin or collodion (the former aqueous, the latter alcoholic), some with the aid of heat, others without. Part of the emulsion was then poured upon plates kept at a moderate temperature and dried. The remainder was boiled or treated with ammonia before being applied to the plates. He also precipitated silver bromide in dilute gelatin or collodion solutions, allowed it to settle completely, washed the precipitate, and mixed it with a new portion of gelatin or collodion before applying it to the plates. Finally he precipitated pure silver bromide, in the absence of all colloids, by means of pure aqueous or alcoholic solutions of bromides and attempted to bring this upon plates, using gelatin or collodion as a cement. The result of all these experiments is that there are essentially two modifications of silver bromide, the one being obtained by precipitation in aqueous, the other in alcoholic solutions. The first, on account of the position of the maximum of sensitiveness for the solar spectrum, he calls blue sensitive, the other, for the same reason, indigo sensitive.

It is of no consequence whether the aqueous or alcoholic solution in which the silver bromide is formed contains gelatin or collodion, or whether the precipitation is effected with excess of bromide or of silver nitrate. It makes no difference whether the solution is hot or cold, or whether the silver bromide is treated with ammonia or whether it is boiled or not. The only necessary condition is that in precipitating indigo sensitive silver bromide the solutions must contain at least 96 per cent of alcohol. From aqueous alcoholic solutions blue sensitive silver bromide is precipitated.

Besides the difference of sensitiveness toward the solar spectrum, these modifications of silver bromide exhibit other characteristic differences in properties which indicate beyond a doubt that they are two essentially different modifications of the same substance. Among these are, 1st. Their unequal divisibility in gelatin or collodion solutions. The indigo sensitive silver bromide cannot be distributed through a gelatin solution, while the blue sensitive modification does so very readily. 2d. Their unequal reducibility; the blue sensitive silver bromide being reduced with much greater difficulty than the indigo sensitive variety. 3d. Their different action toward chemical and physical sensitizers. 4th. Their different action toward photographic developers. 5th. Their different action under the influence of heat. The blue sensitive variety if heated under water has its sensitiveness perceptibly increased, while the other is not changed by such treatment.

A direct transformation of one modification into the other has not yet been accomplished. The effect of the light upon these substances is incipient reduction, and we might hence suppose that the more reducible indigo sensitive variety would be the more sensitive to light. But this is not the case, because it is not chemical reducibility, but the absorption power for light that is of the greatest importance. Now the blue sensitive silver bromide has a greater absorption power than the indigo sensitive variety, and hence its greater sensitiveness. Silver chloride prepared by methods similar to those used in making the two forms of bromides was also found to exist in two modifications. One is designated as ultra violet sensitive, the other as violet sensitive silver chloride.--_Amer. Chem. Jour_.

* * * * *

ANALYSIS OF A SAMPLE OF NEW ZEALAND COAL.

[Footnote: Read before the Society of Public Analysts on the 28th June, 1883.]

By OTTO HEHNER

Some discussion having recently taken place as to the value of New Zealand coal as a fuel, the following results of a somewhat full analysis may be worthy of being placed on record.

The sample to which the results refer consisted of large brownish black lumps, many of which showed woody structure; the fractures were conchyloid, the surface shiny and highly reflecting. It was interspersed with a considerable amount of an amber colored resin. When powdered it appeared chocolate brown. It burned readily, the flame being bright and very smoky. Its ash was light and reddish brown.

It consisted of--

Water (loss at 212° F.) 20.09 Organic and volatile matter 75.19 Ash 4.72 ------ 100.00

The organic and volatile constituents had the following percentage composition--

Carbon 71.26 Hydrogen 5.62 Oxygen 21.58 Nitrogen 1.06 Sulphur 0.48 ------ 100.00

The ash was composed of--

Silica 27.26 Alumina 26.48 Oxide of iron 12.98 Lime 20.19 Magnesia 3.42 Sulphuric acid 9.47 Alkalies and loss 0.20 ------ 100.00

From these figures the composition of the coal itself calculates as under--

Water 20.09 Carbon 53.58 Hydrogen 4.23 Oxygen 16.23 Nitrogen 0.80 Sulphur 0.36 Silica 1.29 Alumina 1.25 Oxide of iron 0.61 Lime 0.95 Magnesia 0.16 Sulphuric acid 0.44 Alkalies 0.01 ------ 100.00

One ton furnished 8,458 cubic feet of gas and 8 cwt. of coke.

The very high proportion of water contained in the sample is very remarkable. It was so loosely combined, that even at ordinary temperature it gradually escaped, the coal crumbling to small pieces. The large amount as well as the high percentage of oxygen characterize the so called coal as a _lignite_, with which conclusion the physical characters of the sample are in perfect harmony.

The resin to which I have referred has not been further analyzed. It was found to be insoluble in all ordinary menstrua, such as alcohol, ether, carbon disulphide, benzene, or chloroform, and neither attacked by boiling alcoholic potash nor by fusing alkali. On heating it swells up considerably and undergoes decomposition, but does not fuse.

The coal may be valuable as a gas coal and for local consumption, but the large proportions of water and of oxygen militate against its use as a steam producer, only 58 per cent. of it being really combustible.

* * * * *

DETERMINING MANGANESE IN STEEL, CAST IRON, FERRO-MANGANESE, ETC.

By E. RAYMOND.

The method in question is recommended as easy, expeditious, and accurate. It consists in precipitating all the manganese in the state of peroxide, dissolving it in a ferrous solution so as to bring back the manganese to the manganous slate, and determining volumetrically, by means of potassium permanganate, the quantity of ferrous salt which has been converted into ferric. The method of rapidly precipitating manganese peroxide is peculiar. If we act upon cast-iron or steel with nitric acid and potassium chlorate in certain proportions, and boil the mixture, the manganese is completely precipitated in the state of peroxide insoluble in nitric acid, but retaining a small quantity of ferric oxide. Suppose that we have a sample of steel or manganiferous cast-iron containing less than 7 per cent of manganese. Three grammes are treated in a small flask with 40 c. c. of nitric acid, of sp. gr. 1.20, added little by little. The liquid is stirred, and ultimately heated to complete solution. It is withdrawn from the fire, and 15 grammes potassium chlorate are added, and then 20 c. c. of nitric acid at sp. gr. 1.40. It is boiled for about fifteen minutes, until the escape of chlorine ceases; all the manganese is found thrown down as peroxide; hot water is added, the mixture is filtered, and the precipitate washed with boiling water. To dissolve the manganese peroxide thus obtained we measure exactly 50 c. c. of an acid solution of ferrous sulphate, made up with 40 grammes ferrous sulphate to 750 c. c. water and 230 c. c. sulphuric acid (full strength). The 50 c. c. are poured into the flask in which the sample has been dissolved, and to which a little peroxide adheres, and it is then poured upon the precipitate and the filter in a Berlin-ware capsule. The manganese peroxide dissolves very readily, transforming its equivalent of ferrous sulphate into ferric sulphate. The liquid is then diluted to 100 or 150 c. c. for the next operation. We then take a solution of permanganate formed by the same proportions as are used in determining iron by the process of Margueritte (5.65 grammes of the crystalline salt per liter of water), and determine its standard exactly. By means of this liquid we determine volumetrically the quantity of ferrous sulphate remaining in the solution of manganese. We take then 50 c. c. of the original solution of ferrous sulphate diluted as above, and determine the total ferrous salt.

The difference between the two determinations corresponds to the ferrous salt which has been peroxidized by the manganese peroxide. The quantity of iron thus peroxidized multiplied by 0.491 gives the quantity of manganese contained in the portion operated upon. In the case of a steel or cast iron containing but little manganese it is convenient to dissolve the peroxide in 25 c. c. only of the ferrous solution. Small Gay-Lussac burettes may then be used in the titration of only 0.010 meter internal diameter, and graduated into one-twentieth c. c., which allows of great exactitude in the determination. For a spiegeleisen not more than 1 gramme of the sample should be taken, and for a ferro-manganese 0.3 gramme.

* * * * *

MANGANESE AND ITS USES.

Manganese is one of the heavy metals of which iron may he taken as the representative. It is of a grayish white color, presents a metallic brilliancy, and is capable of a high degree of polish, is so hard as to scratch glass and steel, is non-magnetic, and is only fused at a white heat. As it oxidizes rapidly on exposure to the atmosphere, it should be preserved under naphtha.

It occurs in small quantity in association with iron in meteoric stones; with this exception it is not found native. The metal may be obtained by the reduction of its sesquioxide by carbon at an extreme heat.

Manganese forms no less than six different oxides--viz., protoxide, sesquioxide the red oxide, the binoxide or peroxide, manganic acid, and permanganic acid. The protoxide occurs as olive-green powder, and is obtained by igniting carbonate of manganese in a current of hydrogen. Its salts are colorless, or of a pale rose color, and have a strong tendency to form double salts with the salts of ammonia. The carbonate forms the mineral known as manganese spar. The sulphate is obtained by heating the peroxide with sulphuric acid till there is faint ignition, dissolving the residue in water and crystallizing. It is employed largely in calico printing. The silicate occurs in various minerals.

The sesquioxide is found crystallized in an anhydrous form in braunite, and hydrated in manganite. It is obtained artificially as a black powder by exposing the peroxide to a prolonged heat. When ignited it loses oxygen, and is converted into red oxide. Its salts are isomorphous with those of alumina and sesquioxide of iron. It imparts a violet color to glass, and gives the amethyst its characteristic tint. Its sulphate is a powerful oxidizing agent.

The red oxide corresponds to the black oxide of iron. It occurs native in hausmannite, and may be obtained artificially by igniting the sesquioxide or peroxide in the open air. It is a compound of the two preceding oxides.

The binoxide, or peroxide, is the black manganese of commerce, and the pyrolusite of mineralogists, and is by far the most abundant of the manganese ores. It occurs in a hydrated form in varvicite and wad. Its commercial value depends upon the proportion of chlorine which a given weight of it will liberate when it is heated with hydrochloric acid, the quantity of chlorine being proportional to the excess of oxygen which this oxide contains over that contained in the same weight of protoxide. When mixed with chloride of sodium and sulphuric acid it causes an evolution of chlorine, the other resulting products being sulphate of soda and sulphate of protoxide of manganese. When mixed with acids, it is a valuable oxidizing agent. It is much used for the preparation of oxygen, either by simply heating it, when it yields 12 per cent. of gas, or by heating it with sulphuric acid, when it yields 18 per cent. Besides its many uses in the laboratory, it is employed in the manufacture of glass, porcelain, and kindred wares.

Manganic acid is not known in a free state. Manganate of potash is formed by fusing together hydrated potash and binoxide of manganese. The black mass which results from this operation is soluble in water, to which it communicates a green color, due to the presence of the manganate. From this water the salt is obtained _in vacuo_ in beautiful green crystals. On allowing the solution to stand exposed to the air, it rapidly becomes blue, violet, purple, and finally red, by the gradual conversion of the manganate into the permanganate of potash; and on account of these changes of color the black mass has received the name of mineral chameleon.

Permanganic acid is only known in solution or in a state of combination. Its solution is of a splendid red color, but appears of a dark violet tint when seen by transmitted light. It is obtained by treating a solution of permanganate of baryta with sulphuric acid, when sulphate of baryta falls, and the permanganic acid remains dissolved in the water. Permanganate of potash, which crystallizes in reddish purple prisms, is the most important of its salts. It is largely employed in analytical chemistry, and is the basis of Condy's Disinfectant Fluid.

Manganese is a constituent of many mineral waters, and is found in small quantities in the ash of most vegetables and animal substances. It is always associated with iron.

Various preparations of manganese have been employed in medicine. The sulphate of the protoxide in doses of one or two drachms produces purgative effects, and is supposed to increase the excretion of bile; and in small doses, both this salt and the carbonate have been given with the intention of improving the condition of the blood in cases of anæmia. Manganic acid and permanganate of potash are of great use when applied in lotions (as in Condy's Fluid diluted) to foul and fetid ulcers. In connection with the medicinal applications of manganese it may be mentioned that manganic acid is the agent employed in Dr. Angus Smith's celebrated test for the impurity of the air.

It is the glass maker's soap of glass manufacture, and is used to correct the green color of glass, which is owing to the presence of protoxide of iron. This it converts into the comparatively colorless peroxide.

It is also used in the Bessemer and similar processes, to decompose the oxide of iron. Spiegeleisen, an iron which contains a natural alloy of from 10 to 12 per cent. of manganese, is used for this purpose when conveniently attainable.--_Glassware Reporter_.

* * * * *

OZOKERITE, OR EARTH-WAX.

By WILLIAM L. LAY.

ON THE DEPOSITS OF EARTH WAX (OZOKERITE) IN EUROPE AND AMERICA.

[Footnote: Abstract from a paper read before the New York Academy of Sciences.]

There exists a large mining and manufacturing industry in Austria, that of ozokerite, or earth-wax, which has nothing like it in any other part of the known world, an industry that supplies Europe with a part of its beeswax, without the aid of the bees. It may not be generally known that the mining of petroleum was a profitable industry in Austria long before it was in this country. In 1852, a druggist near Tarnow distilled the oil and had an exhibit of it in the first World's Fair in London. In America, the first borings were made in 1859. Indeed, the use of petroleum as an illuminator was common at a very early age in the world's history. In Persia at Baku, in India on the Irawada, also in the Crimea, and on the river Kuban in Russia, petroleum has been used in lamps for thousands of years. At Baku the fire worshipers have a never-ceasing flame, which has burned from time immemorial. The mines of ozokerite are located in Austrian Poland, now known as Galicia. Near the city of Drohabich, on the railway line running from Cracow to Lemberg, is a town of six thousand inhabitants, called Borislau, which is entirely supported by the ozokerite industry. It lies at the foot of the Carpathian Mountains. About the year 1862, a shaft was sunk for petroleum at that place. After descending about one hundred and eighty feet, the miners found all the cracks in the clay or rock filled with a brown substance, resembling beeswax. At first, the layers were not thicker than writing paper; but they grew thicker gradually below, until at a depth of three hundred feet they attained a thickness of three or four inches. Upon examination, it was found that a yellow wax could be made of a portion of this substance, and at once a substitute for wax was manufactured.

The discovery caused an excitement like the oil fever of 1865 in America. A large number of leases were made. When I saw the wells of Pennsylvania, in 1879, there were more than two thousand. The owner of the land received one-fourth of the product, and the miners three-fourths. In the petroleum region, the leases at first were whole farms, then they were reduced to 20, then 10, then 5, and at last to 1 acre, which is a square of 209 feet.

But in the ozokerite region of Poland, where everything is done on a small scale, when compared with like enterprises in this country, the leases were on tracts thirty-two feet square. These were so small that the surface was not large enough to contain the earth that had to be raised to sink the shaft; consequently the earth had to be transported to a distance, and, when I saw it, there was a mound sixty or seventy feet high. Its weight had become so great that it caused a sinking of the earth, and endangered the shafts to such an extent that the government ordered its removal to a distance and its deposit on ground that was not undermined. The shafts are four feet square, and the sides are supported by timbers six inches through, which leaves a shaft three feet square. The miner digs the well or shaft just as we dig our water wells, and the dirt and rock are hoisted up in a bucket by a rope and windlass. But one man can work in the shaft at a time. For many years no water was found; but, as there is a deposit of petroleum under the ozokerite, at a depth of six hundred feet from the surface, the miners were troubled with gas. This is got rid of by blowing a current of fresh air from a rotary fan through a pipe extending down the shaft as fast as the curbing of timber is put in place. The ozokerite is embedded in a very stiff blue clay for a depth of several hundred feet; below, it is interlaid with rock. [Specimens of crude and manufactured ozokerite were on exhibition, through the kindness of Dr. J. S. Newberry.]

That part of the earth's surface has more miners' shafts to the acre than any other part of the globe. As wages are very low in Poland, averaging not more than forty cents a day for men and ten cents for children, a very small quantity of ozokerite pays for the working. If thirty or forty pounds a day is obtained, it remunerates the two men and one or two children required to work each lease. When the bucket, containing the earth, rock, and wax, is dumped in the little shed covering the shaft, it is picked over by the children, who detach the wax from the clay or rock with knives. The miners use galvanized wire ropes and wooden buckets. When preparing to descend, they invariably cross themselves and utter a short prayer. The business is not free from danger, carelessness on the part of the boy supplying the fresh air, or the caving in of the unsupported roof, causing a large number of deaths. One of the government inspectors of the mines informed me that in one week there had been eight deaths from accidents.

The ozokerite is taken to a crude furnace, and put into a common cast iron kettle, and melted. This allows the dirt to sink to the bottom, and the ozokerite, freed from all other solids, is skimmed off with a ladle, poured into conical moulds, and allowed to cool, in which form it is sold to the refiners, for about six cents per pound. The quantity produced is uncertain, as the miners take care to understate it, for the reason that the government lays a tax upon all incomes, and the landowner demands his one-fourth of the quantity mined. The best authority is Leo Strippelman, who states the quantity produced in fifteen years at from 375,000,000 to 400,000,000 pounds, worth twenty-four millions of dollars. As the owners of the land get one-fourth of the sum, they received six millions. This is at the rate of four hundred thousand a year, a rather valuable crop from some two hundred acres of land.