GEOPHYSICAL LABORATORY. 167 



and 70 per cent of akermanite, while the pseudowoUastonite solutions extend 

 to a composition containing about 23 per cent of the same compound. 



(5) The presence of an area of solid solution which includes the wollas- 

 tonite-diopside, the wollastonite-akermanite, and the wollastonite-5CaO. 

 2Mg0.6Si02 solid solutions. The decomposition temperatures on this area 

 between the 17 per cent diopside sohd solution and the compound 5CaO.- 

 2Mg0.6Si02 pass through a minimum. 5Ca0.2Mg0.6Si02 decomposes at 

 1365° C. and the 17 per cent diopside soHd solution at about 1340° C., while 

 pure wollastonite inverts at 1200° C. 



In addition to the results just mentioned, which suffice to clear up the 

 liquidus relations in question, as thorough an investigation as the nature of 

 the problem and the available methods of attack would permit was carried 

 out upon the solid solutions of siHca and 3Ca0.2Si02 in calcium metasihcate 

 and upon the inversion and decomposition temperatures of all the various 

 soHd solutions. 



A general discussion of these results, with diagram and models, is given. 

 The formation of unstable phases in sihcate melts is also discussed, and the 

 futihty of attempting to use formulas derived from the theory of dilute solu- 

 tions in order to calculate the change of inversion temperature with sohd 

 solution is briefly mentioned. 



(25) Use of optical pyrometers for control of optical-glass furnaces. Clarence N. Fenner 



BuU. Am. Inst. Min. Met. Eng., 1001-1011 (1919). (Papers on Optical Glass, 

 No. 13.) 



Among the features of careful control required in the manufacture of optical 

 glass, that of the regulation of furnace temperatures is of high importance. 

 During most of the time that a pot of glass is in the furnace the temperature 

 should be allowed to vary but httle in either direction from that which has 

 been found to be appropriate for the given stage of operation. It is therefore 

 of great importance to have available a rehable means for the rapid determina- 

 tion of such temperatures. During the early experiences of the Laboratory 

 in optical-glass making, it was perceived that the thermo-couples generally 

 in use did not come up to the requirements of the case, and it was thought 

 that optical pyrometers should be a satisfactory substitute. Before adopting 

 them for general use, tests were made to determine to what degree the re- 

 quirements were satisfied. Two principal questions were investigated: 

 first, the correctness of the cahbration table supphed with each instrument, 

 and second, the degree to which radiation from furnace-walls agrees with 

 that of a ''black body," or a body whose intensity of luminosity corresponds 

 to its temperature. The method of carrying out these tests is described in 

 some detail, as similar tests are desirable wherever optical pyrometers are 

 installed. As a result, it was found that the manufacturer's cahbration tables 

 were considerably in error in some cases (which impUes that they should 

 always be checked), and that the luminosity of furnace- walls agrees satisfac- 

 torily with that of a "black body" under some conditions but departs very 

 widely under others. The reason for these results and the factors upon which 

 they depend are discussed. The manner in which the pyrometer is used 

 under working conditions is described. The conclusion is reached that when 

 the readings of the pyrometer are properly checked by such tests as these the 

 instrument gives a very satisfactory and rehable means of controlling furnace 

 temperatures. 



(26) The cooling of optical glass melts. Howard S. Roberts. J. Am. Ceram Soc 2 



543-563 (1919). (Papers on Optical Glass, No. 14.) '' ' 



The conditions to be attained when a melt of optical glass is cooled in the 

 pot are: (1) that neither ream nor bubbles shall be introduced during the 



