GEOPHYSICAL LABORATORY. 143 



much more positive and less affected by impurities than in any of the other 

 methods. Complete details are given both of the method of preparing the 

 ore for titration and of carrying out the titration. 



(9) The iodometric determination of sulfur dioxide and the sulfites. John B. Ferguson. 



J. Am. Chem. Soc, 39, 364-373 (1917). 



Before an extended investigation of volcanic gases could be carried out, some 

 problems in analytical chemistry required solution, and in this paper are pre- 

 sented and discussed the results of an investigation of the various iodometric 

 methods for the determination of sulphur dioxide and the sulphites. The 

 object of this investigation was threefold: (1) To ascertain the limitations 

 of the existing methods and procedures; (2) to determine the important 

 sources of error; (3) to develop, if necessary, procedures suitable for general 

 application. 



Sulphur dioxide. — Of the methods considered, the excess iodine is suitable 

 for the analysis of mixtures of either high or low sulphur-dioxide content; the 

 Selby Smelter Commission method is suitable for mixtures of low sulphur- 

 dioxide content; the Reich method gives onlj^ approximate results unless large 

 samples are available ; and the sulphite method must not be used mthout a cor- 

 rection factor. Two precautions are essential: (1) The gas sample m.ust not 

 come in contact with even a trace of moisture prior to reaching the absorbent; 

 (2) the analyzing apparatus must be free from rubber connectors if mixtures 

 containing 2 per cent or more of sulphur dioxide are to be analyzed ; and rubber 

 connectors would best be eliminated altogether. The excess iodine method is 

 recommended. 



Sulphites. — In the Treadwell method errors due to the oxidation of the sulphite 

 solution arise from various sources and to eliminate them the following pro- 

 cedure is recommended : The solid salt is dissolved directly in an excess of 

 an iodine solution containing sufficient hydrochloric acid, and the excess iodine 

 determined Avith thiosulphite. 



(10) The setting of litharge-glycerine cement. H. E. Merwin. J. Ind. Eng. Chem., 9, 



390 (1917). 

 The setting of this cement is caused by the formation of acicular crystals 

 growing in felty masses. The crystals have the composition C3H602.PbO, 

 and indices of refraction a = 1 .75 ; 7 = 1 .80 ; /3 = 1 .84. Larger grains of litharge 

 become protected by coatings of the crystals and remain undecomposed for 

 an indefinite time. 



(11) A convenient form of autoclave. George W. Morey. J. Wash. Acad. Sci., 7, 205-208 



(1917). 

 This paper contains a description of a new type of autoclave which has 

 proven advantageous in the study of aqueous solutions at temperatures up 

 to 300°. 



(12) The ternary system HjO-KsSiOs-SiOa. George W. Morey (Chemical Study) and 



C. N. Fenner (Microscopic Study). J. Am. Chem. Soc, 39, 1173-1229 (1917). 



The system whose study is described in this paper differs materially in 

 several important particulars from practically all heterogeneous equilibria here- 

 tofore studied . Because of the presence of the volatile component water it is sub- 

 stantially different from the systems previously investigated in this laboratory, 

 which were composed of non-volatile oxides and could therefore be treated as 

 "condensed" systems. On the other hand, it differs from all aqueous systems 

 l-)reviously studied in that the "solubility" or fusion relations have been studied 

 under conditions of pressure and temperature far removed from ordinary 



