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X.—Chapters on the Mineralogy of Scotland. Chapter Second.—The Felspars. 
Part I. By Professor Heppiz. (Plates XVII., XVIII.) 
(Read 15th April 1877.) 
Before submitting the results of my examination of the silicates, it is incum- 
bent upon me to give an outline of the processes adopted for their analysis, 
seeing that the amount of confidence which is to be placed in the results must 
rest very immediately thereupon. 
1. Determination of the Water.—In all silicates which were found, after 
thorough drying, to give out moisture when heated in the closed tube, the 
amount of loss upon ignition was calculated as water. About 2 grammes, 
crushed in the diamond mortar, were first merely heated throughout in the air- 
chamber of a water-bath, the contact temperature of which was 212° Fahr., 
the temperature of the air-space being never below 199°. The weight after this 
heating was taken; and, except in the case of a mineral functioning in any 
peculiar way, the loss in weight was estimated as hygroscopic moisture. The 
mineral was now continuously heated in the bath until the weight was found to 
‘be constant. It was then exposed for the space of one hour to a full red heat, 
in the flame of a Bunsen burner, after which it was re-weighed. Finally, it was 
exposed for ten minutes to a heat approaching whiteness, in a three-jet GriFFIN 
blast-furnace,* again re-weighed, and again heated in this furnace, until the 
weight was constant. 
It was found that minerals which contained any considerable quantity of 
water, lost markedly different proportions thereof during the three latter stages 
of this treatment. 
2. Determination of the “ Silica” and the Bases—The minerals were decom- 
posed in the ordinary way by fusion with 43 times their weight of FREzENtrus’ 
flux. The fritting and fusion occupied one hour in a Bunsen flame; the cru- 
cible was then heated for ten minutes in the GRIFFIN furnace. 
Although the exposure of the platinum crucibles to these naked flames was 
found destructive to a very considerable extent, still it was not by any means so 
much so as the necessary exposure in a GrirFin draught-furnace proved to be. 
FLETCHER’s furnace, with plicated copper burner, was discarded after two 
* I cannot too highly recommend this simple and cheap little furnace ; it commands every tem- 
perature, and, for mineral analysis, is superior to all others which require a blowing apparatus. 
VOL. XXVIII. PART I. 3 F 
