1108 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the aid of sulphuric acid. The powdered mineral, of which 1 mgrm. 

 is sufficient, is heated to dryness with sulphuric acid in a platinum 

 dish. The residue is treated with water, and a drop of the solution 

 placed on a slide. Certain tests demonstrate the presence of basic 

 constituents in solution. In the residue are found gypsum^ the in- 

 soluble sulphates of barium and strontium ; these are dissolved in 

 strong sulphuric acid, and crystallize out on cooling. 



The characteristics of microcrystals would be unsatisfactory and 

 imperfect if their optical properties were left out of consideration. 

 Therefore, with the study of crystal forms which aid the analysis of 

 any substance, examination of crystals by polarized light must be 

 associated. The optical characteristics of microcrystals gain in im- 

 portance because, while their angular measurement does not attain 

 the same distinctness as in the larger crystals, yet the optical 

 anomalies of microcrystals are more rare than those of the large. 



Dr. Haushofer's arrangement of the subject matter of his work is 

 alphabetical. This, if not strictly scientific, at least saves all trouble 

 of hunting for a given subject, and any compound can be found at 

 once. The text is copiously illustrated by woodcuts of crystal forms 

 of almost infinite variety. 



In this connection it may be noted that Dr. J. L. W. Thudichum, 

 in a discussion * on " Medico-legal and Chemical Microscopy," con- 

 siders that in all cases chemical tests should be relied upon, crystal- 

 line form not being trustworthy evidence, for it frequently happens 

 that these forms are determined by impurities present, so that often 

 the substance in its pure form cannot be made to crystallize at all. 

 Even when substances form definite crystals, these vary in appearance 

 according to the mass of the substance used, the heat, and other circum- 

 stances. The microscopical detection of octahedral crystals is merely 

 a confirmation of the presence of arsenic, but not diagnostic, since 

 other substances produce similar crystals. Dr. Thudichum also con- 

 siders that the micro-spectroscope has no advantage over the ordinary 

 spectroscope, since both require the same amount of material to pro- 

 duce definite results. The Microscope is especially useful in the 

 preliminary stages of an inquiry ; thus, in dealing with 1500 ox 

 brains, he had found it invaluable in preparing phrenosine from these. 



Examining Diamonds and Cut Gems.j — In the microscopical 

 examination of diamonds and cut gems the best results are obtained 

 when they are submerged in glycerin or balsam. A temporary cell, 

 large enough to contain the gem, is easily made by cutting or punch- 

 ing a hole in a cake of ordinary white wax, and it is firmly attached 

 by heating the slide slightly. Small gems may thus be examined 

 without removing them from their settings. The cell should be 

 entirely filled with the mounting fluid and a cover-glass applied. 

 Canada balsam gives better effects with most gems than glycerin does, 

 but the difficulty of cleaning it off makes the latter preferable. 



* Eugl. Mech., xlii. (1885) pp. 219-20. 



t St. Louis National Druggist, vii. (1885) p. 197. (Microscopy, by Dr. 

 F. L. James.) 



