GEOPHYSICAL LABORATORY. 159 



acid by evaporation with sulphuric acid and subsequent filtration; and finally 

 proceeding as outlined in (2). 



These methods for arsenic in glasses are generally appHcable to substances 

 in which the arsenic can be transformed into sulphide without loss, and are 

 highly accurate. 



A comparison of the iodometric method and the magnesium pyroarsenate 

 method for arsenic in glass is made. The former has the advantage in accu- 

 racy and also in speed, except where occasional determinations are called for. 



Boric acid. — For the determination of boric acid we have found that Chapin's 

 method is very rehable and yields highly accurate results. It has been shown 

 that in order to obtain very accurate results a "blank" must be made and the 

 value apphed as a correction to the amount of boric acid found. The cor- 

 rection is small and for ordinary work can be neglected. The accuracy of the 

 method is \exy appreciably afi"ected by relatively large amounts of arsenious 

 acid, but not by arsenic acid. Boric acid can therefore be satisfactorily 

 determined in the presence of large amounts of arsenious acid by oxidizing 

 the solution with H2O2 after making it distinctly alkaHne with NaOH. 



Relatively large amounts of fluorides appreciably affect the accuracy of 

 the determination, but do not seriously impair its usefulness for ordinary work. 



Other determinations. — Our experience with the following cases in glass 

 analysis is detailed: (1) the determination of the minute quantities of iron in 

 optical glass ; (2) the separation and determination of zinc ; (3) the separation 

 and determination of lead and barium when they occur together; (4) the 

 separation of calcium or barium from relatively large quantities of aluminum 

 occurring with almost no iron; (5) the determination in boric-acid glasses of 

 those elements with which the boric acid interferes. 



Attention is called to the universal presence of hygroscopic moisture in 

 powdered glass samples. Some data by Mr. E. S. Shepherd on gases in glass 

 are given. 



(3) The condition of arsenic in glass and its r6le in glass-making. E. T. Allen and E. G. 



Zies. J. Am. Ceram. Soc, 1, 787-790 (1918). (Papers on Optical Glass, No. 6). 



Analyses show that in all the glasses tested, both plate and optical glasses, 

 the major part of the arsenic present exists in the pentavalent state, but 

 nevertheless a portion exists in the trivalent state. It appears that arsenic 

 trioxide is oxidized at a low temperature and the product formed is stable 

 enough to remain until a high temperature is reached and the glass becomes 

 fluid, when it slowly dissociates into oxygen and arsenic trioxide, both of which 

 aid in the fining. 



(4) The ternary system CaO-MgO-Si02. J. B. Ferguson and H. E. Merwin. Proc. Nat. 



Acad. Sci., 5, 16-18 (1919). 



A brief preUminary report upon the results of an extended study of this 

 ternary system. (See abstracts (23) and (24), below.) 



(5) Silicate specific heats. Second series. Walter P. 'WTiite. Am. J. Sci., 47, 1-43 (1919). 



Specific heats of various forms of siHca and sihcates have been determined 

 for upper temperatures from 100° to 1400°. The method was by dropping 

 from furnaces into calorimeters. A rather unusual number of checks and 

 precautions against error was employed, which are described in detail. Two 

 new methods are described for determining true or atomic heats from interval 

 heats. 



On the whole, the general temperature variation of the specific heats is one 

 depending mainly on the value of v, the atomic vibration period, for oxygen in 



