180 H. L. Wells — Double Salts of Lead Tetrachloride. 



The principal components of the light bands are actinolite of 

 the platy form, grains of a light green amphibole that may be 

 a more ferriferous actinolite, and a few ragged grains of plagio- 

 clase. None of these constituents have sharp outlines. They 

 all dovetail into one another even more irregularly than do the 

 minerals of a granitic rock. In the little interstices that some- 

 times occur between the larger individuals and included within 

 these in considerable quantity are many small and more or less 

 rounded grains of a colorless mineral, whose isotropic sections 

 show the straight bar of a uniaxial interference figure. Other 

 sections are rhomboidal in shape. These are doubly refracting 

 and they extinguish parallel to the diagonals of the rhomboids. 

 The general aspects of the mineral, and its properties, so far 

 as they can be determined, are those of quartz. 



The descriptions above given agree very closely with those 

 given by Irving and Yan Ilise* for the corresponding schists 

 in the Penokee series, except that in the Minnesota rocks 

 quartz is rare and hematite is absent. The presence of these 

 peculiar rocks in the Mesabe range is noteworthy, since their 

 origin in certain other districts is supposed to be very closely 

 connected with the origin of the iron ores with which they 

 are associated. If in the Mesabe district they are found to be 

 related genetically with an original carbonate of iron, an 

 important analogical link between the Mesabe and the Penokee 

 series will have been established. 



Art. XX VI. — On some Double Salts of Lead Tetrachloride ; 

 by H. L. Wells. 



The existence of lead tetrachloride has long been surmised 

 from the fact that the corresponding oxide, when dissolved in 

 cold hydrochloric acid, gives a yellow solution in which sul- 

 phuric acid does not give an immediate precipitate. Lead 

 tetrachloride itself, however, has never been isolated, nor has 

 any double salt which it forms been satisfactorily described. 



Sobrero and Selmif found that when chlorine is passed into 

 a solution containing sodium chloride and lead chloride, the 

 liquid becomes yellow. They found it impossible to isolate 

 the compound either by evaporation or cooling, so that they 

 determined the lead, sodium and chlorine in such a solution, 

 and found it to contain these constituents in the ratio corre- 

 sponding to PbCl 4 +9NaCl. Sobrero and Selmi say that per- 



* R. D. Irving and C. R. Yan Hise : 1. c, p. 389-393. 

 f Ann. China. Phys., Ill, xxix, 1G1. 



