282 CARNEGIE INSTITUTION OF WASHINGTON. 



employed in Harvard University in order to make a preliminary deter- 

 mination of the atomic weight. The samples were small and for various 

 reasons the results can not be considered as anything more than pre- 

 liminary, but the outcome is, nevertheless, worth recounting. In the 

 last and best determination 0.43947 gram of gallium chloride (weighed 

 in vacuo in a sealed glass tube) yielded 1.07087 grams of silver chloride, 

 having required 0.80587 gram of silver for complete precipitation. 

 The atomic weight of gallium computed from these two sets of data are 

 respectively 70.09 and 70.11; the concordant results indicate a value 

 somewhat higher than that usually accepted for gallium, but near 

 enough to show that the chloride was at least not far from being pure 

 and that the whole proceeding is capable, when employed with larger 

 quantities of material and with the experience already gained, of 

 affording an accurate evaluation of this atomic weight. At the con- 

 clusion of the war it is hoped that Mr. Craig will be able to com- 

 plete the investigation. 



5. Purification of Gallium by Electrolysis. 



With the help of Mr. Sylvester Boyer, various other methods for 

 purification of gallium were studied in detail. The method recom- 

 mended by various authorities, of separating gallium from indium by 

 means of the different solubilities of the hydroxids in caustic alkali, 

 was tested without great success. The separation was found to be so 

 incomplete that a considerable percentage of indium remained in the 

 gallium, at least under the conditions used in our work, and it seemed 

 clear that this difference in solubility is not enough to effect a complete 

 separation. Much more promising results were obtained by the elec- 

 trolytic method. Galhum occupies a place in the electrolytic series 

 between indium and zinc. It is far less easy to deposit than indium, 

 but much more easy to deposit than zinc. By carefully regulating the 

 hydrogen-ion concentration and current density it was possible to 

 deposit practically all of the indium with only a little gallium, and 

 thereafter most of the gallium could be separated in a slightly acid 

 solution without the appearance of an important amount of zinc. 

 Gallium obtained in this way, from material which had previously been 

 purified by the hydroxide method, melted at a temperature as high as 

 30.8°, a higher melting-point (indicating a purer substance) than is 

 recorded anjnvhere in the literature. The metal obtained by the hy- 

 droxide process, without electrolysis, melted at a temperature as low 

 as 26.9°. Time has as yet been lacking for making complete spectro- 

 scopic and other tests of this material in order to confirm its complete 

 purity, but enough has been done to show that this method is very 

 satisfactory and convenient. Because of its obvious advantages it 

 must have been employed before by others, but no mention has yet 

 been found of it. 



