CHEMISTRY. (ANALYSIS.) 



155 



ties of gluoinnra chloride and bromide. The 

 determination places glucinum in the same 

 class as carbon, boron, and silicon. It also 

 affords a striking argument in favor of the 

 value of deductions drawn from the periodic 

 law in regard to the atomic weight of an ele- 

 ment, and shows that such deductions will in 

 future form one of the most important factors 

 in fixing a doubtful atomic weight. 



Halberstadt has determined the atomic 

 weight of platinum after Seubert's experi- 

 ments from the double chlorides of potassium 

 and of ammonium respectively, and also from 

 the corresponding bromides and platinum te- 

 trabromide. Two methods of analysis were 

 employed, in one of which the platinum was 

 determined by igniting the compound in a cur- 

 rent of hydrogen ; in the other by electric pre- 

 cipitation. Ninety-seven determinations were 

 made 59 by ignition, and 38 by electrolysis 

 the mean result of all of which was 197*57592. 



Thorpe has determined the atomic weight of 

 titanium, in one series of experiments from the 

 tetrachloride, and in a second series from the 

 tetrabromide. The reagent used was water 

 or silver. The mean result gave 48, which 

 corresponds with the number in Mendelejeff's 

 table, as the most probable atomic weight. 



Analytical Chemistry. For both the qualita- 

 tive and quantitative determination of silver 

 in lead-ores, Jean Krutwig decomposes from 

 twenty to twenty -five grammes of the lead-ore 

 in an iron crucible with borax, soda, and cream 

 of tartar. The lead thus obtained, which con- 

 tains, besides iron and sulphur, all of the silver, 

 is dissolved in concentrated nitric acid, water 

 is added, and the lead sulphate is filtered off. 

 The filtrate is then treated with an excess of 

 caustic soda and allowed to stand for some 

 time, after which the brownish-yellow precipi- 

 tate, containing iron, lead, and silver, is fil- 

 tered. This precipitate, which consists of lead 

 and iron hydroxide and a so-called plumbite of 

 silver, is then treated on the filter with a some- 

 what concentrated solution of ammonia, which 

 dissolves the plumbite of silver. The ammonia 

 is expelled from the filtrate by evaporating on 

 the water-bath, and the residue is dissolved in 

 nitric acid. The silver is then detected, either 

 by treating with caustic soda solution, and thus 

 obtaining' the characteristic precipitate of sil- 

 ver plumbite ; or by precipitating the lead as 

 sulphite, filtering, and treating the filtrate with 

 hydrochloric acid. 



H. Reinsch has called attention to the use 

 of the microscope as affording an important 

 means of qualitative chemical analysis. It re- 

 quires, however, great skill in manipulation, 

 for the effects are liable to vary according to 

 the degree of concentration of the solutions 

 used. Silica yields the most varied and beau- 

 tiful forms, resembling plants and ferns, and 

 often presents, in the most glowing colors, 

 fine-leaved flower forms in infinite varieties. 

 The forms are obtained by adding to a drop of 

 a 4 per cent, solution of potassium silicate on an 



object-slide a drop of 2 per cent, solution of 

 sodium bicarbonate, and allowing the liquid 

 to evaporate ; if 1 per cent, of sodium bicar- 

 bonate is added instead of 2 per cent., the 

 flower-forms are not obtained, but polarized 

 spheres appear under the Nicol prism. The 

 most minute traces of silica can be readily de- 

 tected in a mineral by this means. Aluminum 

 oxide, glucina, and boric acid, are also easily 

 detected. The alkalies possess optic proper- 

 ties, by which they can be definitely and cer- 

 tainly distinguished with the microscope. Their 

 sulphates are most suitable for examination. 

 Ammonium sulphate assumes peculiar shapes 

 that can not be confounded with those of 

 any other salt. Lithium sulphate forms clus- 

 ters of prismatic needles that exhibit striking 

 polarization effects. Barium assumes mossy, 

 glistening, colorless dendritic forms, while 

 strontium nitrate takes the form of radiating 

 needles, with colors changing under the po- 

 larizer. Magnesia may be detected by its 

 colorless clusters of needles, even when pres- 

 ent in the most minute quantities. Cadmi- 

 um assumes more characteristic, and uranium 

 more beautiful forms, than any others of the 

 metals. The cadmium sulphate produces large 

 spheres containing ellipsoids, which radiate 

 Irom the center, and are marked by regular 

 transverse depressions, and which present most 

 brilliant and remarkable effects under the 

 Nicol prism. The formation assumed by the 

 uranium sulphate, which can readily be rec- 

 ognized by the pocket lens, resemble beau- 

 tifully colored asters, or corn-flowers. Less 

 frequently, the salt appears in the form of 

 envelopes with velvet-blue narrow and purple- 

 colored broad triangles, which also may be 

 recognized without the Nicol prism. Other 

 characteristic forms have been described for 

 lime, potassium, copper, manganese, iron, mer- 

 cury, and silver sulphates. 



The fatty oils differ so little from one an- 

 other physically that their examination is dif- 

 ficult. MM. Doumet and Thibaut indicate a 

 method of spectrum analysis for which the 

 oils are divided according to their absorption- 

 spectra into four groups : (1) those which have 

 the spectrum of chlorophyl, among which are 

 included olive, hemp, and nut oils ; (2) those 

 which transmit all rays equally, and have con- 

 sequently no spectrum of these are castor oil, 

 and the expressed oils of sweet and bitter al- 

 monds ; (3) oils which absorb all the " chemi- 

 cal " or more refrangible rays, and have a 

 characteristic spectrum. In this group we 

 find rape, colza, mustard, and linseed oils. In 

 the fourth group the absorption extends in 

 bands over the more refrangible part of the 

 spectrum, but is not complete. In it are the 

 oils of sesame, earth-nuts, and poppy- seed. 



The processes heretofore in use for the sep- 

 aration of resin from the fats and the quanti- 

 tative estimation of the substance are defective, 

 because the solvents for oleic acid and its salts 

 and for the resins are to a considerable extent 



