M. Carey Lea — Allotropic forms of Silver. 47 



may possibly have been produced from the same original 

 magma. 



At some future time the locality will be revisited with the 

 expectation of finding the rock in place and exposed in a way to 

 permit of the study of any modifications of structure the rock 

 mass may undergo. It will, I think, be found to occur as one 

 of the intrusive dikes cutting the earlier andesitic lava sheets 

 and broad fields of breccias. Ishawooa Canon lies north of 

 the Leucite hills about 150 miles, the geological conditions 

 being quite different from those surrounding the earlier known 

 locality. 



In columns 2 and 3 of the table will be found analyses from 

 the two other American localities of leucite-bearing rocks. In 

 column 4 of the table the analysis of a leucite-basalt from the 

 Eifel, described by Hussak, is given for the purposes of com- 

 parison, it corresponding more closely in chemical composition 

 to the Ishawooa rock than any other published analysis. It 

 is, however, like most leucite rocks, richer in alkalies with 

 potash in excess of the soda. 



Akt. V. — On Allotropic Forms of Silver ; by M. Caeey Lea. 



[Continued from page 491, vol. xxxvii.] 



In the first part of this paper were described certain forms 

 of silver ; among them a lilac-blue substance, very soluble in 

 water with a deep red color. After undergoing purification it 

 was shown to be nearly pure silver. During the jmrification 

 by washing it seemed to change somewhat, and consequently 

 some uncertainty existed as to whether or not the purified sub- 

 stance was essentially the same as the first product : it seemed 

 possible that the extreme solubility of the product in its first 

 condition might be due to a combination in some way with 

 citric acid, the acid separating during the washing. Many at- 

 tempts were made to get a decisive indication and two series of 

 analyses, one a long one, to determine the ratio between the 

 silver and the citric acid present, without obtaining a wholly 

 satisfactory result, inasmuch as even these determinations of 

 mere ratio involved a certain degree of previous purification 

 which might have caused a separation. 



This question has since been settled in an extremely simple 

 way, and the fact established that the soluble blue substance 

 contains not a trace of combined citric acid. 



The precipitated lilac-blue substance (obtained by reducing 

 silver citrate by ferrous citrate) was thrown on a filter and 

 cleared of mother water as far as possible with a filter pump. 



