Chemistry and Physics. 207 



SCIENTIFIC INTELLIGENCE. 



I. Chemistey and Physics. 



1. Perchloric Acid as a Dehydrating Agent in the Determina- 

 tion of Silica.— U. H. Willard and W. E. Coke, of the Univer- 

 sity of Michigan, have found that the nse of perchloric acid gives 

 marked advantages over the usual methods for this very 

 frequently required analytical determination. The dihydrate 

 of perchloric acid, HCIO4.2H0O, boils at 203 °C, and at this tem- 

 perature is a powerful dehydrating agent. Nearly all its salts 

 are soluble in the strong acid and in water, presenting in this 

 respect a great advantage over sulphuric acid for this purpose. 

 The pure acid has been on the market for some time, and 

 although still rather expensive it could be made more cheaply 

 if there were sufficient demand for it. 



The method as applied consists in dissolving the metal or 

 silicate in hydrochloric or nitric acid, adding perchloric acid, 

 or dissolving directly in perchloric acid, evaporating to dense 

 fumes of the latter, boiling gently, in a covered beaker to avoid 

 undue waste of the acid, for 15 or 20 minutes to dehydrate the 

 silica, cooling and diluting with water. All salts are instantly 

 soluble and the silica is filtered off and determined as usual. 

 It contains less impurity than when separated by the usual 

 methods. Moreover the silica remaining in solution is much less 

 than in the usual method of evaporation to dryness and treat- 

 ment with hydrochloric acid, so that except for the most accurate 

 work it can be neglected. The operation is simple and rapid. 

 Test analyses made by the authors upon very pure quartz sand 

 (after fusion with sodium carbonate), upon cements, limestones, 

 samples of willemite, irons, steels, aluminium and nickel gave 

 very good results.. It seems probable that this new method will 

 fincl extensive application, both in scientific and technical analy- 

 sis. — Jour. Amer. Chem. Soc, 42, 2208. h. l. w. 



2. The Chemistry and Crystallography of Some Fluorides of 

 Cobalt, Nickel, Manganese and Copper. — It is sometimes desir- 

 able, perhaps, to call attention to a chemical article for the pur- 

 pose of showing that it is unsatisfactorily presented. Such 

 appears to be the case in this article by Floyd H. Edmister 

 and Hermon C. Cooper, which takes up about 15 pages of an 

 important chemical journal. They have described the acid 

 fluorides 



C0F2.5HF.6H.O, 



NiF,.5HF.6H;0, 



MnF,5HF.6H,0, 



and CuF2.5HF.6H;0. 



