GEOPHYSICAL LABORATORY. 169 



The complications, usually almost negligible, arising from specific heat, 

 uneven temperature, and other causes are considered, and suitable experi- 

 mental arrangements are suggested. 



(10) A practical test for the resistance of optical glass to weathering. F. Russell v. Bichow- 



sky. J. Am. Ceramic Soc, 3, 296-304 (1920). (Papers on Optical Glass, 

 No. 23a.) 



The experiments described in this paper were made in 1917 with the object 

 of getting a rapid routine method for testing the weather stability of the 

 optical glasses then being made for miUtary purposes. There was no oppor- 

 tunity to make long-time tests under conditions to be met in the field, although 

 such tests should underlie any future exhaustive investigation to correlate 

 weathering resistance with routine laboratory tests. 



The surface-alkali test described by Mylius was used, but its indications are 

 not certain for all types of glasses. Methods of determining the rate of 

 solubiUty in water, ammonia, or hydrochloric acid were also tried, but were 

 not found adaptable for routine procedures. The tests finally adopted con- 

 sisted in heating samples of the glass, in company with a standard glass, in 

 water, 5 per cent sodium hydroxide, and 1 : 1 hydrochloric acid, at tempera- 

 tures of 175° or 225° C. The glasses could then be classified into 9 groups 

 according to their appearance when wet and when dry, although there is 

 sometimes considerable difference in the order of stabiUty found with the three 

 reagents used. The safest estimate is one based on the three tests taken as 

 a group. 



The results of these tests were compared with the results by the surface- 

 alkah and rate-of-solubiUty methods. 



(11) Note on the mechanics of the "weathering" of glass. F. Russell v. Bichowsky. J. 



Am. Ceramic Soc, 3, 309-312 (1920). (Papers on Optical Glass, No. 23b.) 



The mechanism of the weathering of a glass surface by water is believed to 

 consist in the following stages: (1) True adsorption; (2) diffusion of adsorbed 

 water into the glass; (3) reaction with the silicates; (4) soaking-up of more 

 water by the film so produced; (5) extraction of the soluble salts; (6) solution 

 of the siUca skeleton. The appearance and behavior on heating of glasses in 

 each of these stages are described. 



(12) Chemical researches on sediments. Herbert E. Merwin. Bull. Geol. Soc. Amer., 31, 



419-424(1920). 



The purpose of this paper is to discuss in a general way various phases 

 of the chemical problems connected with the study of sedimentary rocks. 

 The problems in general are difficult because of the complexity of the solu- 

 tions, the sUght solubility and the lack of definite crystallinity of many of the 

 substances, and the persistence of unstable phases. 



Diffusion in the solid state, consolidation under differential stress, adsorp- 

 tion, slow reactions, and effects of catalysis are discussed both in general and 

 with respect to such problems as the formation of dolomite and phosphate 

 rocks, and the oceanic red clay. 



(13) The manufacture and uses of rolled optical glass. H. S. Roberts and J. C. Hostetter. 



J. Am. Ceramic Soc, 3, 750-761 (1920). (Papers on Optical Glass, No. 24.) 



Rolled optical glass is manufactured by a process that combines the stirring 

 and earlier processes used for ordinary optical glass with the casting and sub- 

 sequent processes ordinarily used in the manufacture of rolled plate-glass. 

 The glass obtained is characterized by the presence of strise in the form of 

 plane-parallel films, which are in general invisible unless viewed edgewise. 

 Optical systems manufactured from rolled glass should therefore be so de- 



