CONSTITUTION OF AMMONIUM AND ITS DERIVATIVES.

Valuable to the science of chemistry as the theory of equivalence has been, it has yet very much to do before it can be admitted to be complete. Indeed, the signs of the times point to a period not very distant when it will be merged into some higher and broader generalization. Chemists are not now agreed, for example, upon a point which would seem to lie at the very foundation of such a theory: namely, whether the equivalence of an element is a fixed quantity for that element, or whether it can vary. In the case of nitrogen, for example, all are agreed that it may and does act as a triad in ammonia; but in ammonium chloride, NH,Cl, where it is combined with five monad atoms, all are not willing to concede that it is quinquivalent. Meyer and Lecco have sought to throw some light upon this question by a careful study of the compound ammoniums. If two of the four atoms of hydrogen in ammonium chloride be replaced by ethyl and two by methyl, two isomeric bodies can be formed if the nitrogen be a triad-thus N(CH3)2C2H5+C2H¿Cl and N(C2H5)2CH3+CH3C1; while, if it be a pentad, these bodies, prepared even though they be in different ways, must be identical. The former of the two was prepared from dimethylamine, and the latter from diethylamine; and the compounds themselves as well as their derivatives were subjected to the most careful scrutiny, but not the smallest dif ference could be observed between them. A critic having suggested that possibly a rearrangement of atoms within the molecule having taken place caused this similarity, the authors specially tested the matter, but with a negative result. They maintain, therefore, that the equivalence of nitrogen in ammonium is five, and that equivalence is variable.-35 C, VIII., 233, March, 1875.

WHY DOES PLASTER OF PARIS SET?

Landrin has examined the chemical and physical changes which are produced in the setting of plaster of Paris. He notices that three separate actions take place, and that these may very readily be observed under the microscope. They are: First, the burned plaster in contact with the water assumes a crystalline form. Second, the water which envel

ops the crystals takes up in solution considerable calcium. sulphate. Third, a portion of this water being evaporated by the heat resulting from the chemical combination, a crystal is formed which determines the crystallization of the whole mass, just as when a crystal of sodium sulphate is dropped into a supersaturated solution of that salt. It is not, however, until after some time that the mass acquires its maximum hardness, the plaster then containing the required proportion of water, i. e., two molecules to one of the calcium sulphate. This amount of water does not lessen by evaporation. In mixing plaster, only about 12 per cent. of water should be added, as ordinary plaster itself contains about 8 per cent.; but in actual practice the amount used is never less than 33 per cent. This excess is added in order to prevent setting of the mass before it can be used. But the effect is injurious, since very porous, slowly drying plasters are produced in this way, which rapidly determine nitrification. To diminish the rapidity of setting is to delay the crystallization, which can be effected by adding gum, gelatin, guimauve powder, glycerine, and similar bodies. Inert substances, like sand and barium sulphate, for example, on the other hand, simply diminish the solubility of the material, without in the least retarding the setting process. Overburned plasters may be utilized by admixture with ordinary plaster, since the crystallization of the latter extends to the former, and occasions the setting of the entire mass. A similar effect is produced by simply mixing the two plasters together. Lime acts favorably upon plaster, as it not only increases the rapidity with which it sets, but it gives it an additional hardness. Plasters to which 10 per cent. of lime has been added are capable of taking a polish. Samples have been made containing as high as 75 per cent. of lime; they are hard and light, and may yet serve some useful purpose in the arts.-6 B, LXXIX., 658.

CONSTITUTION OF GUM TRAGACANTH.

Giraud has made a minute examination of the chemical characters of gum tragacanth. He finds (1) that this gum is but very slightly soluble in water, and that the product in the filtrate is not a definite principle like arabin, but is a mixture of several substances; (2) that digested on the wa

ter-bath for twenty-four hours, with fifty times its weight of water, much of it is transformed into a soluble gum, which no longer swells after drying: this new substance is pectin; (3) that under the action of water containing one per cent. of acid, the production of pectin takes place in two or three hours. It becomes entirely soluble, and alcohol precipitates pectin, not arabin, from the solution. Alkalies change it into pectates and meta-pectates. Hence gum tragacanth consists for the most part of a pectic principle insoluble in water, apparently identical with Fremy's pectose. From it by precip itating the pectin solution by barium hydrate and decomposing by an acid, pure pectic acid was obtained. Upon analysis, gum tragacanth yields as follows: Water, 20 per cent.; pectic compounds, 60 per cent.; soluble gum, 8 to 10 per cent.; cellulose, 3 per cent.; starch, 2 to 3 per cent.; mineral matter, 3 per cent.; nitrogenous matters, traces.-4 B, III., v., 361, April, 1875.

CARBONYLES, A NEW CLASS OF ORGANIC BODIES.

Berthelot has recently instituted a new class of organic bodies, to which he has given the name Carbonyles, and to which he assigns three bodies hitherto rather ambiguous in their chemical behavior. These are allylene oxide, dipheny lene acetone, and ordinary camphor, to which he gives the new names dimethylene carbonyle, diphenylene carbonyle, and terebutylene carbonyle. The distinguishing feature of carbonyles is their double function. In the first place they act like aldehydes, being able to fix hydrogen directly and to produce alcohols; while they are themselves reproduced, like aldehydes, by hydrogenization of these alcohols. Again, like aldehydes, they may be formed by the direct or indirect oxidation of hydrocarbons; camphene hydride and oxygen producing camphor precisely as ethylene hydride and oxygen produces common aldehyde. But, secondly, it is to be observed that while aldehydes are produced by the indirect oxidation of saturated hydrocarbons, carbonyles result from the indirect oxidation of unsaturated hydrocarbons. This is a very material difference, since, besides its aldehydic function, the carbonyle molecule is itself unsaturated for this very reason, and hence can combine directly with other saturated molecules. Like the radical carbonyl itself, from

which these bodies take their name, they can therefore fix directly the elements of water and form monobasic acids; dimethylene carbonyle uniting with water directly and yielding propionic acid. Moreover, by virtue of this unsaturation they can unite directly with three atoms of oxygen to form dibasic acids; camphor yielding camphoric acid in this way. Conversely, the removal of water and carbonic dioxide from a single molecule of a dibasic acid yields a carbonyle; thus differing from the analogous production of ketones, by the fact that in the latter case the removal is from two molecules of a monobasic acid. The author gives evidence to show that camphor belongs to this class of bodies, and says that, had he not hesitated to found a new class of bodies on a single compound, he would have proposed camphor as a carbonyle long ago.-Bulletin de la Société Chimique de Paris, II., xxiii., 146, February, 1875.

HÆMATIN NOT FERRUGINOUS.

It has been for some time known that the proportion of iron which existed in the coloring matter of the blood, called hæmatin, was very variable, and that by repeated purification it could be so far reduced in amount that only a trace remained. Hence the opinion has arisen that the iron is not an essential constituent, as is generally supposed. Paquelin and Jolly have examined the question at length, starting from the well-known researches of Chevreul upon this substance, which were to the same purport. The results have shown the correctness of the assumption, they having succeeded in devising a process by which the whole of the iron may be removed and the hæmatin obtained pure. In brief their method is as follows: Having removed the albuminates of the blood by basic lead acetate, the corpuscles are dried and powdered, then digested in glacial acetic acid until they are reduced to a gelatinous mass. The coloring matter is then taken up by carbon disulphide or benzene, and the hæmatin recovered by careful evaporation of the solvent. The corpuscles may with advantage be macerated in alcohol containing ten per cent. of ammonia previous to the treatment with acetic acid. The purification of the hæmatin from the iron is the next step. It is dissolved in ten times its weight of acetic acid, two and a half parts of citric

acid dissolved in a little water is added, and the whole is brought to boiling to favor the colution of the iron. To the cooled liquid, ammonia is added in quantity sufficient to exactly neutralize the acids, and the precipitated hæmatin allowed to subside. This treatment is repeated so long as ammonium sulphide discovers in the supernatant ammoniacal liquid any trace of iron. The purified hæmatin is finally dissolved in ether, the solution filtered, and the ethereal liquid allowed to evaporate spontaneously. The pure coloring matter is insoluble in water, slightly soluble in alcohol, but readily so in ether, chloroform, carbon disulphide, and benzene. It burns on platinum like a resinous substance, without leaving any trace of ash.-6 B, LXXIX., 918.

FORMATION OF SULPHATES BY GAS FLAMES,

A white incrustation is always formed after a short time on the glass covers hung over gas flames. This incrustation consists of small crystals of normal ammonium sulphate, with a trace of soda and potash. The sulphur in the gas which is burned to produce the sulphuric acid does not exist in the condition of hydrogen sulphide, but in that of carbon disulphide. The ammonia is not a product of combustion, for if a basin whose lower surface is moistened with hydrochloric acid be held over a gas flame, there are no fumes visible, and no ammonia is found even with the delicate reagent of Nessler. But unburned gas contains a small quantity of ammonia, enough to give a yellow color with the Nessler test. Priwoznick has investigated this question, and supposes that the ammonia comes from the nitrogen of the air, for Saussure has shown that ammonia is formed when hydrogen is burned in oxygen containing nitrogen. Schönbein proved the pres ence of ammonium nitrate in the products of combustion of fat and of coal-gas. The carbon disulphide in the gas would burn to carbonic and sulphurous dioxides. But sulphurous oxide can not exist in presence of ammonium nitrite, but is immediately oxidized to sulphuric acid and combines with the ammonia. The glass cylinder of an argand lamp is also often covered with a white incrustation. This consists mainly of potash, soda, lime, etc., from the ash of particles of dust in the air.-14 C, CCXIII., 223.