62 CONTRIBUTIONS TO MINERALOGY. [bull. 262. 
It is, however, not true that Hidden and Mackintosh neglected to 
take account of the ferrous iron, etc., of their analysis. It was 
regarded in the derivation of their empirical formula R 2 Si 2 7 . How 
wholly unwarranted was the substitution by Benedicks of his formula 
for yttrialite is shown by the molecular ratio for RO: R 2 3 :Si0 2 , which 
he gives as 1:2:4 instead of 1:3.25:7.42, as calculated by me from 
Mackintosh's figures, wherein for a sound reason I have converted hi 
UO. { into U0 2 , thus throwing it with the Th0 2 , where it naturally 
belongs. The agreement is indeed "gar nicht gut." 
Benedicks has made the grave mistake of counting Mackintosh! 
monoxide bases a second time, thus making a basic salt R"R'" 4 Si 4 0| 
instead of the normal one R'" 4 Si 4 O u , to which Mackintosh's results 
closely conform. 
DISCUSSION OF BENEDICKS'S FORMULA FOR THALENITE, 
Moreover, in the light of the data furnished by Benedicks himsek 
it can not be admitted that the formula H 2 Y 4 Si 4 15 for thalenite i; 
established. 
Water was determined by him according to Penfield's method/' bu 
without any hint as to the particular modification employed. If, ai 
seems probable, the water expelled from the mineral was caused a 
recondense in the cooler part of the ignition tube, the latter bein< 
then weighed, and again after driving the condensed water out, tw< 
serious sources of error have to be considered: (1) The C0 2 present i 
the mineral, which would count in part as water unless a very carefu 
correction was made, as provided for by Penfield. No mention i 
made by Benedicks of any such correction. (2) Nitrogen and heliur i 
are said to comprise 1.4 per cent of the mineral by weight. If sc 
these would introduce an error in the above water determination c I 
contrary sign to that due to C0 2 , and if the proportion of helium wen 
large this error might be of very considerable magnitude. 
In an appendix to his paper Benedicks gives an analysis of what 1 
considers to be a very pure form of thalenite. He makes no compa 
ison of this with his earlier analysis, nor does he deduce a molecuh 
ratio, which I find to be 1:2.6:5.15, or 1:3.03:6.02 if small amount] 
of lime, magnesia, and soda are neglected, instead of 1:2:4, as require 
by his formula. There being no C0 2 in this purer material, the vah 
for water (if determined as above surmised) ma} r be supposed to 1 < 
affected only by the error due to nitrogen and helium. It will 1 
seen that the neglect to regard lime, magnesia, and soda in his secoi 
analysis affects the ratio very seriously. This neglect may be justitii < 
in figuring on his first analysis because of an approximate balanciiij 
by C0 2 , but it would be by no means so in the other, in spite of t 
very satisfactory ratio obtained and leading to the empirical formi 
«Am, Jour, Sci., ser. 3, vol. 48, 1894, p. 31. 
