100 



CHEMISTRY. 



arsenic in considerable proportions the pink, 

 which had tha least, having enough on a 

 square foot to poison an adult person. By the 

 side of these papers were placed, for compari- 

 son, six other samples obtained from another 

 manufacturer, the colors of which could hardly 

 be distinguished from those of the arsenical 

 papers, but which were wholly free from 

 arsenic. From these and other papers which 

 were compared with the same object, it was 

 found that almost any color that may be de- 

 sired can be obtained without the addition of 

 that substance. If any difference exists in the 

 appearance of the arsenical and non-arsenical 

 colors, it is that the former are rather brighter. 

 This, however, is not altogether a merit, for 

 wall-colors may very easily be too bright. It 

 is still undetermined whether the cheaper or 

 more expensive papers usually contain more 

 arsenic, and also in which class it is more com- 

 monly found. 



AMMONIA IN HUMAN SALIVA. Mr. B. H. 

 Heyward, of the laboratory of the University 

 of Virginia, has made some researches into the 

 presence of ammonia in human saliva. Evi- 

 dence of the presence of the alkali was ob- 

 tained by observing the action of heated oxide 

 of magnesium upon filtering-paper moistened 

 with the Nessler reagent. The paper showed 

 a distinct orange tint when saliva was present, 

 but was not affected when the saliva was omit- 

 ted. In all of nineteen different cases exam- 

 ined, of as many young men in good health, 

 the ammonia reaction was obtained. In ten 

 of the cases the amount was approximately de- 

 termined to be in proportions varying from 

 thirty to one hundred milligrammes of am- 

 monia per litre of saliva. The proportions in 

 the mixed saliva of a single person varied, on 

 seven successive days, between forty and sixty 

 milligrammes per litre. Special experiments 

 directed to the different salivary glands indi- 

 cated that most, if not all, of the ammonia 

 came from the parotid and subrnaxillary glands, 

 the latter furnishing notably the larger share, 

 and that the source of ammonia at any rate, 

 the sole or chief source is not to be found as 

 free gas in the expired products of respiration 

 condensed in aqueous solutions in the mouth. 



GUM-LAO FROM ARIZONA. A resinous sub- 

 stance has been found widely distributed 

 throughout Arizona and Southern California, 

 where it forms a coating of considerable thick- 

 ness on the twigs of the Larrea Mexicana, or 

 "greasewood," which exhibits the cellular 

 cavities containing ova of insects, and at cer- 

 tain seasons a red fluid, and other characteristic 

 properties as to color, solubility, the color given 

 to different solutions, action under the influence 

 of heat, and odor, of the gum-lac of India. An 

 analysis of the substance, by J. M. Stillman, of 

 the University of California, gives its composi- 

 tion as consisting of 61 '7 parts of resins, 1:4 of 

 coloring matter soluble in water, 26'3 of caustic 

 potash extract, 6*0 of insoluble residue, with a 

 loss (including some coloring matter) of 4'6. 



This shows a near correspondence, as to essen- 

 tial elements, with the composition of the 

 Indian shellacs. A gum is also found, but 

 in smaller quantities and having a less amount 

 of coloring matter, on the twigs of the Acacia 

 Greggii, which resembles the lac from the 

 Larrea in its general appearance and irregular 

 cellular structure, as well as in its essential 

 chemical properties, and behaves in the same 

 manner toward chemical reagents. 



THE FREEZING-POINT OF ALCOHOLIC MIX- 

 TURES. Researches which have been made by 

 M. Raoult, of the Faculty of Sciences at Greno- 

 ble, on the point of congelation of alcoholic 

 liquors, show that the point at which mixtures 

 of alcohol and water begin to freeze falls as the 

 proportion of alcohol becomes stronger. M.., 

 Raoult has made a table of the points of con- 

 gelation for different mixtures, by a compari- 

 son with which the strength of any given 

 mixtures may be determined by subjecting 

 them to the freezing-test. Fermented liquors 

 congeal at a temperature a little lower than 

 mixtures of alcohol and water of the same 

 strength, the difference increasing as the pro- 

 portion of alcohol becomes stronger. In all 

 cases the ice consists of pure water, wholly 

 free from alcohol. Hence the part of the 

 liquid left unfrozen is richer than the original 

 liquid, and it follows that the point of conge- 

 lation descends as the congelation progresses. 



A NEW THEORY OF STEEL. Mr. W. Mattieu 

 Williams has proposed a new theory to account 

 for the temperability of steel. It is well known 

 that, if steel is heated red-hot and suddenly 

 cooled, it becomes extremely hard and brittle ; 

 if heated again and slowly cooled, it becomes 

 almost as soft and tough as wrought-iron. If 

 it is moderately heated, it becomes partially 

 softened or "tempered," in proportion to the 

 temperature to which it is raised. None of 

 these properties is possessed by either of the 

 materials, carbon or iron, of which the steel is 

 composed. Mr. "Williams's theory is based on 

 the fact that there exists a definite compound, 

 consisting of four equivalents of iron to one of 

 carbon, which may be obtained in crystals, and 

 which is more fusible than ordinary steel, and 

 far more fusible than iron, and is excessively 

 hard and brittle, but not temperable like steel. 

 When it is melted at a temperature at which 

 iron is quite infusible, it is capable of dissolving 

 iron, and forming a liquid mixture. When 

 such a mixture is cooled below the solidifying 

 point of one of the substances, while its tem- 

 perature is still above that of the other, then 

 one must be still fluid while the other is striving 

 to solidity. " If the cooling beyond this goes 

 on slowly, the molecular conflict will have 

 time to settle itself; but, if the cooling is ef- 

 fected suddenly, there must be a 'molecular 

 strain,' due to the inequality of contraction of 

 the different parts of the solid and the liquid 

 portions of the mixture, the internal fluid 

 movements necessary for the adjustment of 

 this irregular contraction of the different parts 



