A. H. Chester on Variscite from Arkansas. 295 



containing only elements of the hydrogen group has a molecular 

 volume an even multiple of that -f hydrog> n. This is probably 

 but a hint of some more general regularity connecting other 

 elements and other groups. 



pub 



hi. — Since the above pages were written, there has 

 lished by Johnson a density determination for potas- 

 iodide, KI 3 . (Chem. News, xxxiv, 256.) This deter- 

 mination. 84!^. corresponds to a molecular volume of 120*1. 

 121 is an exact multiple of 5*5, and gives a theoretical density 

 of 3 472. The multiple relation now holds good in twenty 

 cases out of twenty-five. 



Art. XXXIV.— On the identify of tin. *,-r df, 1 Peg an ite of Arkan- 

 sas with the Varisnitr of Brathaupt and Callaimle of Damour ; 

 by Albert H. Chester. 



A number of years ago I obtained some specimens of a 

 mineral, said to come from Colorado, which, after a hasty ex- 

 amination, was called peganite. More recently, I have received 

 specimens of the same mineral from Montgomery County, 

 Arkansas, from which locality the first undoubtedly came. 

 Analyses were made of both, with the results given below ; 

 No. 1 is of the amorphous mineral, and No. 2 is the average 

 alyses of the crystalline variety. It was found impos- 

 separate it from "the quartz \ 



sible to separate it from the quartz with 



and a considerable quantity of the latter substance is unavoid- 

 ably included in each analysis. 



Phosphoric acid... 13-08 22*36 



Alumina .. • 9*59 15*72 



Water 7*08 11*89 



Insoluble residue 69-69 49-86 



Total, 99" 44 99 " 83 



Deducting the insoluble residue, and calculating to one hun- 

 dred percent, we have the results below in columns 1 and 2, 

 while 3 gives' the average of the two, and 4 the oxygen ratio. 



Phosphoric acid 43-96 44*74 44-35 5'05 



Alumina.... 32-24 31*46 31*85 3'00 



Water 23*80 23'SO 23"80 432 



In four other analyses the ratio of water to phosphate of 

 <^mina was found to be 1 to 4*04, 426, 4*01, and 4*23. The 

 formula for the mineral must then be A1 2 3 , P 3 0.,+4H 2 0, * 

 making it distinct from peganite, with which it has been con- 

 A *. Joub. Sci._Thibd Sebibs, Vol. XIII, No. 76.-Apbil, 1877. 



