A. L. Day and J. K. Clement — Gas Thermometer. 461 



mines sulphur at the same time with arsenic and antimony, by 

 interposing between the generator and the absorption cylinder 

 which contains the silver nitrate another cylinder containing 

 potassium-cadmium cyanide which absorbs all the hydrogen 

 sulphide and according to him retains no arsenic and antimony. 

 Since a solution of this cadmium compound is always alkaline, 

 it was thought safer to take a separate portion of zinc for the 

 estimation of sulphur, silver nitrate being used as the absorp- 

 tion reagent. The small precipitate was examined for sulphur 

 by dissolving in nitric acid and proceeding as usual. Found 

 (M m e BaSO;. Blank gave 0*3 ra s BaS0 4 . 



The zinc was tested for silicon in the same way as the 

 copper. 



Redeterminations with other metal samples. — The zinc, 

 silver and copper melting points were redetermined in 1908 

 with other metal samples from the same sources as before and 

 serve to show the accuracy which may be expected in random 

 samples of the same (nominal) purity. The gold was not 

 redetermined for the reason that no second charge was avail- 

 able, nor indeed was a redetermination deemed necessary.* 

 Complete analyses of these samples have not been made, but 

 such tests as were undertaken serve to show that the copper 

 was even purer than that of which the analysis is given. The 

 results of these determinations are shown in the following 

 table : f . 



1908 Metal -W^Ticro^lta Temperature 



March 10. Zinc 3404- 418-58 



March 12 Silver in CO 9055- 958*78 



April 10 CopperinCO 10476' 1081*5 



Following are the most probable values of the metal melting 

 points : 



Zinc 418*5°± 0-1° 



Silver 958*3 ± 0*5 



Gold 1059*3 ± 1*0 



Copper _ 1081*0 ± 0*5 



Summary. 



The gas thermometer problem at the present stage of its 

 development has become primarily a problem for experimental 

 study with two definite purposes, one to increase the accuracy 



* Sometime after our work with gold had been completed a reexamination 

 of the charcoal which had been used to cover the surface of the metal during 

 melting, very unexpectedly yielded iron. The gold was also found slightly 

 contaminated with iron. The gold point here offered is, therefore, no longer 

 entirely above suspicion and will now be repeated as soon as a fresh charge 

 can be obtained. The probable error is accordingly given much larger than 

 the original measurements indicated. 



f Determinations by E. B. Sosman. 



