﻿84 Canadian Record of Science. 



The ratio (RaO + CaO) : (Mg, Mn, re)0 is, as observed 

 by Scharizer in the case of the Jan Meyen and Bohemian 

 hornblendes, approximately 3 : 4, thus : 



Including Water. Excluding Water. 



(RoO + CaO) : (Mg, Mn, Fe)0. (R^O + CaO) : Mg, Mn, Fe)0. 



Jan Meyen 3 : 3-87 3 : 4-17 



Bohemia 3 : 4-10 3 : 4-10 



Stenzelberg .... 3 : 4 02 3 : 4-38 



Dungannon. . . . 3 : 3*84 3 : 4-11 



Scharizer adopts the following ratios (3:1:3 and 3 : 4) 



as those of syntagmatite in calculating the composition 



I n III 

 of hornblendes intermediate between (R2B)3 B^SigOia and 



actinolite. He assumes in the first place that all the alumina 

 and ferric oxide belong to the syntagmatite molecule (2). The 

 sum of the AL^Oa and Fe^Og molecules (from the molecular 

 ratio) multipled by three, gives (SiO.^)^ on the one hand 

 and (RP + R'0)2 on the other. The sum of (RgO + RO)^ 

 divided in the proportion of 3 : 4 gives (R2O + CaO)2 and 

 MgO + FeO)2. Subtracting (MgO + FeO)2 from the sum 

 of tlie corresponding molecules deduced from the analyses 

 gives (MgO + FeO)^ — that is the number of molecules of 

 magnesia and ferrous oxide belonging to the actinolite 

 molecule (A) — and MgO + FeO)^ divided by three (see 

 actinolite formula) gives the lime molecules of the actino- 

 lite (CaO)^. This value subtracted from the total number 

 of lime molecules gives (CaO)2, and (CaO)2 subtracted 

 from (RaO + CaO)^ gives the alkali molecules (in some 

 cases including HgO). Finally (MgO -f- OaO)^ gives (SiOa)^. 

 These statements will be made clearer by the following 

 example, one of those selected by Scharizer. 



