CHEMICAL MICROSCOPY 



feebl}^ basic and partly acidic compounds, 

 and those of high solubiHty in water. 



Inorganic Precipitation with Re- 

 agents for Basic Nitrogen. Potassium and 

 ammonium have similar solubilities for their 

 salts, and so give similar precipitation reac- 

 tions; and, in a more general view, the al- 

 kaloids and other compounds of basic ni- 

 trogen react much like the heavier alkali 

 metals. Cesium (ion) is precipitated by most 

 of the "alkaloidal" reagents and rubidium 



> 



\ 



N^sr-^ n 



Fig. 7. Sodium bromaurate crystals. Na2S0 

 (solid) with HAuBr4 in H3PO4 . 



Fig. 8. Magnesium bromauraurate crystals 

 MgCl.-eHsO (solid) with HAuBr4 in H3PO4. (Pho- 

 tographed with red-sensitive plate.) 



by perhaps a third of them, from aqueous 

 solution. The most general of such reagents 

 often precipitate ammonium and potassium; 

 and conversely, a reagent used to precipitate 

 potassium is worth trying as a general pre- 

 cipitant of nitrogenous bases. 



Sodium ion is not precipitated from aque- 

 ous solution by the "alkaloidal" reagents, 

 but in a medium of syrupy phosphoric acid 

 the relationship of the lighter elements be- 

 comes apparent. Not only sodium, (Fig. 7) 

 but even lithium, magnesium (Fig. 8), zinc, 

 and cadmium, become more or less subject 

 to such precipitation. Even the hydrogen 

 compound verges on insolubility, and for 

 example bromauric acid itself, HAuBr4 , will 

 precipitate from H3PO4 solution with drying. 

 These inorganic reactions have been studied 

 very little, except the formation of bromau- 

 rates. 



Charles C. Fulton 



CHEMICAL MICROCRYSTAL IDENTIFICATIONS 



The microscope should be used throughout 

 chemistry; it is surely an obvious instrument 

 (and not a new one) simply for taking a 

 closer and better look at small things. Chem- 

 ists should turn to it as naturally as to test- 

 tubes or the bunsen burner, whenever it will 

 help. It has applications requiring knowledge 

 and study, too, particularly the polarizing 

 microscope, which is by far the most valu- 

 able. Its especial use, discussed here, is in a 

 basic branch of analytical chemistry— the 

 making of identifications. This is a subsid- 

 iary science in its own right, not well ex- 

 plained by the vague general term "qualita- 

 tive analysis". It is, of course, a part of 

 qualitative analysis, as distinguished from 

 quantitative, but it is a special part, in 

 which we ought to use properties, tests, and 

 reactions especially characteristic, or even 

 specific for individual substances. Physical 

 properties, although obtained by some gen- 

 eral method, are often used when they can 

 be accurately measured in such a way as to 



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