386 Jannasch and Loch: — Water in Topaz. 



Aet. XLY. — On the Presence of Water in Topaz ; by 

 Paul Jannasch and James Locke. 



We give in the following article the first results of an 

 investigation of the mineral topaz, which we have undertaken 

 in connection with our recently published work on the formula 

 of the axinite from Bourg d'Oisans.* As the first step in this 

 investigation w r e subjected the mineral to a careful examina- 

 tion for water, and have found, as the analyses below show, 

 that it contains a very significant quantity of water of consti- 

 tution. 



The method which we employed to detect and estimate the 

 water has been described by us in detail in another article,t 

 but it may be well to explain again its principle and some of 

 the precautions which we took to secure accurate results. The 

 substance was mixed with lead oxide in a bulb-tube and 

 strongly fused over the flame of a Bunsen burner, and the 

 escaping water received in a weighed calcium chloride tube. 

 To retain any traces of hydrofluoric acid or silicon fluoride 

 which might also be evolved, a layer of lead oxide about an 

 inch long was placed in the posterior arm of the bulb-tube. 

 The lead oxide used was in some cases the purest article to be 

 obtained from Merck, in others we prepared it ourselves by 

 precipitating lead acetate with ammonium carbonate, thor- 

 oughly washing by decantation, evaporating to dryness and 

 igniting the residue in a platinum dish. The ignited product 

 was placed, while still warm, over potassium oxide under a 

 bell-jar and kept there when not in use. After being intro- 

 duced into the tube, but before its mixture with the powdered 

 mineral, each portion of lead oxide was freed from the last 

 traces of moisture by gentle ignition in a current of dry air. 

 We watched carefully, in every one of the experiments, for 

 signs of escaping hydrofluoric acid or silicon fluoride, but 

 could detect neither : the glass remained perfectly smooth and 

 unattacked throughout, and the water, which could be plainly 

 seen as it condensed in the cold part of the bulb-tube and in 

 the bulb of the calcium chloride tube, showed no trace of 

 silica. 



The specimens of topaz examined were in every case fresh 

 and well formed crystals, and absolutely free from foreign sub- 

 stances. The analyses cover four varieties, one of which con- 

 tained nearly 3 - per cent of water, the others approximately 

 1*0 per cent. The analytical results follow : 



* Zeitschrift fur Anorgan. Cheurie, Bd. vi, Heft 1. 

 flbid., Bd. vi, Heft 2. 



