abstracts: analytical chemistry 45 



elusions previously announeed, and it is believed that the explanations 

 suggested by the foreign observers are directly at variance with the 

 experimental evidence. The conclusion is reached, as before, that the 

 field of stability of tridymite is limited by the temperature of 1470° =•= 

 10°, and that at higher temperatures up to the fusing point cristobalite 

 is the stable form. C. N. F. 



ANALYTlCAIv CHEMISTRY. — The rapid electrometric determination 

 of iron in some optical glasses. J. B. Ferguson and J. C. Hos- 

 tetter. Journ. Amer. Ceram. Soc. 2: 608-621. Aug., 1919. 

 (Geophysical Lab. Papers on Optical Glass, No. 16.) 



The results of the application of the electrometric determination of 

 iron with stannous chloride and potassium dichromate are discussed 

 in this paper. The electrometric method enables one to make rapid 

 and accurate analyses for both ferric and ferrous iron, provided inter- 

 fering substances are absent. Under favorable conditions, such an 

 analysis can be made in 10 minutes and may be carried out in glass- 

 ware. Four different procedures are described for total iron and one 

 for ferrous iron. A number of analytical results, including many fer- 

 rous-iron determinations, are given. The ferrous-iron content of the 

 glasses proved to be dependent upon a number of factors and in some 

 cases reached values in excess of 35 per cent of the total iron present. 



J. B. F. 



ANALYTICAL CYL^Ml^T^Y .—Determination of free carbon in rub- 

 ber goods. A. H. Smith and S. W. Epstein. Bur. Standards 

 Techn. Paper 136. Pp. 8. 1919. 



After a brief review of the literature, a discussion is given of the 

 difficulties encountered in the use of the nitric acid method. It is 

 shown that nitric acid attacks the carbon and gives an insoluble com- 

 pound, with the result that a factor of 1.05 must be used. An experi- 

 ment is outlined which is taken to prove that bituminous matter is all 

 removed by the treatment indicated. The effects of various mineral 

 constituents are discussed and methods are outlined for their removal. 



The authors conclude that, though the attack of nitric acid on 

 carbon makes a very accurate determination impossible, the error 

 caused thereby when the factor 1.05 is used is sufficiently small 

 to justify the use of this method at the present time as a routine one 

 in the rubber laboratory. S. W. E- 



