12 Annals of the South African Museum. 



alkalies, salts soluble in water and nickel iron was done with 

 separate portions. For dissolving the latter a well-boiled solution 

 of ammonium-mercuric-chloride was used, in such a way that the 

 reaction and filtration took place in an atmosphere of carefully 

 purified hydrogen. ■•= 



1. Composition of silicates soluble in hydrochloric acid : — 



1. 



SiO, = 28-51 61-33 



Al^Oj^ 0-57 1-23 



FeO = 0-47 1-01 



CaO = 0-15 0-32 



MgO = 16-78 36-11 



Cr,03= 0-00 — 



MnO = trace — 



46-48 10000 



If one reckons the metasilicates of magnesium, iron, and calcium, 

 then 0-57 per cent, of Al,03 and 2-85 per cent, of SiO^ remain 

 over. 



But as it is probable that a part of the alkalies belongs to the 

 siHcate which is insoluble in hydrochloric acid, the amount of 

 alumina and a portion of the excess of silica may be explained by 

 the presence of about 3 per cent, of a plagioclase f closely allied to 



* Vide C. Friedheim : Ueber die chemische Zusammensetzung der Meteoi-iten 

 von Alfianello and Concepcion. Sitz.-Ber. d. K. Preuss. Akad. d. Wissensch. 

 Berlin, 1888, and L. Fletcher, Chemical Analysis of the Meteoric Stone found at 

 Makariwa, near Invercargill, New Zealand, in the year 1879. Min. Mag. 1894, X. 

 pp. 288 and 293-295. 



t To the same may then also belong the CaO, by which the quantity of plagio- 

 clase would be somewhat higher. It is true that the presence of plagioclase could 

 not be proved under the microscope, but, as I have already stated, the abundance 

 of opaque ores make the examination of the matrix very difficult. In both cases 

 about \ per cent, of Na^O is taken into account, and there remains then an excess of 

 only 0-84 and 1-56 respectively of silica. This is not too much if one considers 

 that according to the method of reckoning all analytical errors in respect to silica 

 accumulate. At any rate it results that the insoluble silicates may be reckoned for 

 the greater part to an enstatite poor in iron and lime, whose percentage composition 

 follows, under \h. 



16. 



SiOa 59-59 



FeO 1-09 



CaO 0-35 



MgO 38-97 



100-00 



