Combustible Substances. 215 



tratinpr, fragrant, and inflammable fluid. It is 

 one of the most volatile of all bodies, and hardly 

 any thing is so much expanded or contracted by 

 heat and cold. Professor Braun^s experiments 

 show it to be the best fluid for measuring intense 

 degrees of cold ; but it will not answer for the de- 

 gree of heat above animal bodies, as its expan- 

 sion when above this is irregular. It boils in 

 vacuo with a heat less than that of the blood of 

 most animals. On this depends the operation 

 of the pulse-glass, which is a tube with a small 

 bulb at its extremity, containing a quantity of 

 spirit of wine, which, when first put in, is made 

 to boil briskly, that the steam may expel the air : 

 it is then hermetically sealed*, and if the finger 

 or hand is applied, it boils. There is one thing 

 remarkable : if we hold the instrument upright 

 it does not boil easily, but if we incline it ever 

 so little it boils- The fact is, there seems to be 

 a little air left in the tube, which may be neces- 

 sary to facilitate the production of vapour; by 

 inclining the tube we let in this air or elastic 

 fluid, and then the spirit boils. 



Spirit of wine undergoes spontaneous evapo- 

 ration in the air, without leaving any thing be- 

 hind : the vapour burns without smoke, and 

 leaves no excrementitious matter. 



The first remarkable effect of mixture on al- 

 cohol is its mixing completely with water, which 



* That is by melting the glass at one end of the tube, 

 so as in a manner to solder it together. 



