But always containing in solution less or more of a substance composed of equal atoms of carbon and hydrogen, and which separated sometimes in crystals and sometimes in a liquid state. He found farther that oil of wine has the property of combining with bases and forming neutral salts with them; and these salts being examined were found to possess exactly the character of the sulpho-vinates as described by Vogel. He found also that sulphuric acid, which in some of Mr. Faraday's experiments had absorbed about 80 times its volume of olefiant gas, had by this process been partly converted into sulpho-vinic acid. Mr. Hennell has published a subsequent paper on the action of sulphuric acid on alcohol, but as it relates rather to the theory of etherification than to sulpho-vinic acid, the facts which it contains will come under our review in a subsequent part of this volume when treating of sulphuric ether.

Sulpho-vinic acid may be obtained from sulpho-vinate of lead or sulpho-vinate of barytes. The sulpho-vinate of lead may be decomposed by a current of sulphuretted hydrogen gas, and the sulpho-vinate of barytes by means of sulphuric acid. The sulpho-vinic acid thus disengaged may be concentrated Properties, by placing it in an exhausted receiver over a basin containing sulphuric acid. By this process it may be rendered nearly as oily-looking as sulphuric acid, and its specific gravity may be raised as high as 1.319. If we attempt to carry the concentration farther the acid undergoes decomposition, sulphurous acid is disengaged, and sulphuric acid remains mixed with a little etherial oil. It undergoes decomposition also if we raise it to the boiling temperature. When of the specific gravity 1.319 it may be left in contact with cold nitric acid without being decomposed, but when heat is applied, deutoxide of azote is disengaged, and sulphuric acid remains. The same alteration is produced when the sulpho-vinates are treated with nitric acid.

This acid cannot be preserved for any length of time without being altered. After a short time it occasions a precipitate in salts of barytes, though at first no such precipitates appear. All the sulpho-vinates hitherto observed are soluble in water. Most of them crystallize and have a sweetish taste, and their

Chap. I.

Composition.

solutions are not precipitated by the salts of barytes or of lead. They may be exposed for a long time to the air without undergoing decomposition. But when heated they are destroyed, and converted either into sulphates or bisulphates, according to the nature of the salt and the quantity of heat applied.

M. Gay-Lussac showed that sulpho-vinic acid, when decomposed by means of nitric acid, yields twice as much sulphuric acid as remains when a sulpho-vinate is exposed to a red heat. Hence he concluded that the sulpho-vinic acid was the hyposulphuric mixed with some vegetable matter. But Mr. Hennell has shown by direct experiment that this acid is a compound of

so that an atom of it weighs 13.5. It saturates just as much of the bases as half the sulphuric acid which it contains would do. On that account, Mr. Hennell conceives that one-half of the acid in it is saturated with the carbo-hydrogen, and that only the other half is at liberty to combine with bases. But this view of the subject is scarcely compatible with the fact that sweet oil of wine is perfectly neutral, unless it be rendered so by the excess of carbo-hydrogen which it contains. The carbohydrogen contained in sulpho-vinic acid is a compound of 4 atoms carbon and 4 atoms hydrogen. It is therefore analogous to the tetarto-carbo-hydrogen described in the first volume of this work (p. 200), though, as it may be obtained even in a solid state, it is certainly not identical with it. It would appear from this, that carbon and hydrogen are not only capable of forming a variety of compounds by grouping together a greater or smaller number of particles of carbo-hydrogen, as has been explained in a former part of this work (Vol. I. p. 191), but even when the number of atoms is the same, the nature of the compound may be altered by a different mode of arranging the atoms. We may then consider sulpho-vinic acid as a com

It is clear that both the atoms of sulphuric acid are in combina

tion with the atom of tetarto-carbo-hydrogen, otherwise the barytes salts would undoubtedly act upon it and throw down that portion which is not in combination.

SECTION LIII.--OF XANTHIC ACID.

Class I.

Div. IL

This acid was also discovered by M. Zeise. His method History. was as follows: To a solution of potash in alcohol bisulphuret of carbon was gradually added till the alkali was neutralized. By this process xanthic acid was formed, which being combined with the alkali constituted xanthate of potash. This salt crys-tallizes in needles; it is colourless and possessed of considerable brilliancy. When exposed to the air it becomes slightly yellow. Its taste is cooling, sulphureous, and sharp. It is very soluble in water, and yet does not absorb moisture from the atmosphere. It dissolves also in alcohol, and is very slightly soluble in ether. When muriatic acid or sulphuric acid, in a concentrated state, is poured upon this salt no effervescence takes place, but if these acids be diluted with four or five times their weight of water, a liquid separates heavier than water, and having an exact resemblance to an oil. This liquid is xanthic acid.

This acid is transparent and colourless. It is liquid at the Properties. ordinary temperature of the atmosphere, and even when cooled much lower. It is heavier than water, and does not unite with that liquid. When exposed to the air it is soon covered with a white opaque crust. It undergoes spontaneous decomposition when kept under water. Its smell is strong and peculiar, bearing some analogy to that of sulphurous acid. Its taste is acid; it then gives an astringent and bitter impression. It reddens paper stained blue with litmus, and the reddened part soon becomes yellowish-white.

This acid dissolves readily in an aqueous solution of potash, barytes, or ammonia. It disengages carbonic acid from carbonate of potash, and forms xanthate of potash. The other alkaline xanthates may also be made by digesting it on the respective carbonates.

In the open air this acid catches fire from the flame of a candle, and burns with a strong odour of sulphurous acid. When heated in a retort it undergoes decomposition at a temperature much lower than that of boiling water. Common bisulphuret of carbon is formed and an inflammable gas evolved, which has neither the smell of onions nor of sulphurous acid. It readily dissolves iodine. The solution is at first yellow and then becomes brown. But the colour soon disappears, and in

Chap. I.

Composition.

two or three minutes (provided too much iodine has not been added) it assumes the form of an oily opaque liquid, having a light yellow colour. The aqueous liquid above this oily matter contains a solution of hydriodic acid.*

Xanthic acid is characterized by precipitating the salts of copper yellow.

According to Zeise this acid is a compound of

This would make the atomic weight 12-375. But this opinion is not founded upon any analysis of the xanthates, but upon the supposition that the acid is a compound of two atoms bisulphuret of carbon, and one atom of alcohol. For alcohol, as we shall find afterwards, is a compound of 1 atom oxygen, 2 atoms carbon, and 3 atoms hydrogen, so that its atomic weight is 2·875; while that of bisulphuret of carbon is 475. Thus we have

2 atoms bisulphuret of carbon
1 atom alcohol

9.5

2.875

Xanthic oil.

12:375

But this opinion, not being supported by satisfactory analyses, cannot be viewed in any other light than an ingenious conjecture. At least in none of Zeise's papers on the subject, which I have had an opportunity of seeing, is the statement supported by experimental evidence.+

During the distillation of xanthate of potash, a substance comes over which Zeise has distinguished by the name of xanthic oil. It is limpid, has a yellow colour, and a very strong and peculiar smell which adheres long to every substance impregnated with it. Its taste is sweet and sharp. Water dissolves

* Zeise; Ann. de Chim. et de Phys. xxi. 160.

+ The reader will find the composition of this acid stated on Zeise's authority in L. Gmelin's Handbuch der Theoretischen Chemie, i. 328; but not supported by experimental proof, as Gmelin is always in the habit of giving when any exists. I am induced from this to suspect that the statement is founded on experiment, though I know of none. As I have not had an opportunity of seeing all the periodical works on chemistry in Germany, some of Zeise's papers might have been overlooked by me. But this is not likely to be the case with a professor of chemistry in a German university.

it in very small quantity. But it is abundantly dissolved in even very weak alcohol. It has no acid qualities, does not precipitate metallic solutions, burns with a blue flame, and the evolution of much sulphurous acid mixed with carbonic acid.

When the xanthates are distilled they are decomposed, sulphuretted hydrogen, carbonic acid, and xanthic oil being formed, and there remains in the retort a sulphuret mixed with charcoal. Nitric acid and chlorine decompose these salts by destroying the xanthic acid; while diluted muriatic and sulphuric acid decompose them, expelling the xanthic acid. The alkaline

Xanthates are soluble in water, and they give with salts of lead a white, and with salts of copper a yellow, precipitate. With salts of protoxide of mercury and oxide of silver they give brown and black precipitates, or at least they speedily assume these colours.

SECTION LIV.—OF SULPHO-NAPHTHALIC ACID.

Class I,

Div. II.

This acid was discovered by Mr. Faraday in the year 1826, History. and described by him in a paper inserted in the Philosophical Transactions for that year. When concentrated sulphuric acid is left in contact with pure naphthaline, a combination gradually takes place, and if the proportion of naphthaline employed be not too great, a complete solution is obtained when the liquid is diluted with water. When carbonate of barytes is digested with this liquid the uncombined sulphuric acid is converted into sulphate of barytes, while a neutral solution of sulpho-naphthalate of barytes is obtained. By filtering the liquid and evaporating, the sulpho-naphthalate, of barytes may be obtained in imperfect crystals. By dissolving this salt in water, and exactly saturating the barytes in it with sulphuric acid, and then filtering, the sulpho-naphthalic acid is obtained pure in a state of solution. This liquid strongly reddens litmus paper, and has a bitter Properties. and acid taste. When strongly concentrated by heat it assumes a brown colour, and on cooling becomes thick and ultimately solid, and is very deliquescent. The heat being renewed it again melted, began to smoke and was charred, but did not flame. It ultimately gave sulphuric and sulphurous acid vapours, and

left charcoal.

Another portion of the same aqueous solution of sulphonaphthalic acid was placed over sulphuric acid in an exhausted receiver. In some hours it became by concentration a soft white solid, apparently dry, and after a longer period it was hard and brittle. In this state it was deliquescent in the air; but in close vessels it underwent no change in several months.