1872.] Capt. W. A. Ross on Pyrology, or Fire Analysis. 



465 



latter, a fresh bead should be impregnated with a weighed portion of the 

 substance, which should be dissolved as far as possible by an O. P. Then, 

 the bead being rapidly removed from the point of the pyrocone, it should 

 be blown into while red-hot with the jet of the pyrogene, which for that 

 purpose should be advanced so as just to touch the ring of the platinum wire. 

 If the bead be not too cold, the result will be that the whole mass is blown 

 out into a thin clear bubble or vesicle about seventy times its first size, thus 

 presenting a very large surface of the dissolved substance to be operated on. 

 This vesicle should then be held in the operator's open mouth and breathed 

 upon for some time, when, if the alkali has contained even a trace of potash 

 (I percent, of KO affords the reaction), the vesicle will immediately be- 

 come clouded over with a light blue film of the colour of a solution of quinine 

 when held against the light. If only soda be present, the vesicle will 

 remain clear but will begin to deliquesce. Lithia affords a tarnish like that 

 of breath on a pane of glass, and the vesicle does not deliquesce. 



69. This test for potash in presence of soda is so delicate that if two 

 beads, even of borax, one containing a trace of potash, be vesiculated and 

 allowed to remain in a moderately dry room for some time, the one con- 

 taining the potash will in the course of a few hours cloud over, while the 

 other will remain quite clear. 



Determination of Gasss by Vesiculation. 



70. The B vesicle by itself will cloud over after a few minutes, but the 

 appearance then is more white than blue; and if the clouded vesicle be 

 approached to the flame of a spirit-lamp, this white coating is not removed 

 until the flame almost touches it and shrivels the substance of the vesicle, 

 whereas in the case of the addition of a trace of potash, the cloud flies as 

 if by magic when the vesicle is even a considerable distance off. 



71. The addition of chlorine to the B bead, made by dipping the bead 

 in strong hydrochloric acid and treating as in paragraph 48, apparently 

 causes the vesicle made therefrom to be still more sensitive to the action of 

 gases upon its surface. It clouds over in common air almost the instant 

 it is made. If held over a solution of ammonia, this nubilescence is pre- 

 vented, and the vesicle remains clear. If held in a noxious or putrescent 

 gas, creamy or brownish-white streaks are formed over the surface, which 

 is otherwise clear. But the most characteristic reaction is that afforded by 

 sulphuretted hydrogen, in an atmosphere of which this vesicle becomes 

 rapidly pitted with circular spots as though it had suddenly taken smallpox. 

 These spots through a lens are observed to be round radiated crystals, with 

 a yellowish tinge near the circumference. After a short time, they rot into 

 holes. 



72. Another curious result of vesiculation is the crystallization of the 

 surface in a moderately damp atmosphere in the course of ten or twelve 

 hours. Borax- vesicles show these best ; but the complicated nature of the 

 salts formed renders conclusions from their crystallization very uncertain. 



vol. xx. 2 m 



