TOL. XLIII.] PHILOSOPHICAL TRANSACTIONS. 14Q 



of water in polishing of glass or marble, and the greasing or oiling all manner of 

 wheel-machines, many of which, for want of that application, have heated, taken 

 fire, and been even consumed in flames of their own exciting. There is no ex- 

 periment, by which it appears, that any the least degree of heat has been gene- 

 rated by the simple or mere mechanical agitation or friction of the particles of any 

 fluid, either by itself, or mixed with various fluids ; water, wine, vinous spirits, 

 oils, quicksilver, either agitated singly or mixed, will by no force, or velocity of 

 motion ever heard of, produce heat ; nor can the blood of animals, when once 

 let out of the body, be kept either fluid or warm by any of the most violent agi- 

 tation. Indeed heat is generated in fluids in some particular circumstances, as 

 in those two so commonly known cases of fermentation and effervescence ; which, 

 as they are frequently confounded by persons not thoroughly versed in chemical 

 matters. Dr. M. explains the difference. 



Fermentation is that spontaneous intestine motion, which, in the degree of 

 heat of the universal temperature of subterraneous caverns, will, in a few hours, 

 bring on such a change in vegetable juices, or in water charged with a strong 

 tincture of vegetable particles (for fermentation is confined to the vegetable king- 

 dom solely) as from a vapid must or wort quenching fire, to make it become 

 more or less inflammable and nourishing of fire, as it is impregnated with more 

 or fewer of the vegetable particles, and in the alembic to afford that volatile subtil 

 inflammable liquor commonly called vinous spirits. The heat produced by fer- 

 mentation never exceeds that of the human body. 



Effervescence arises from an intestine motion, to be excited in various sorts of 

 fluids, either by the mixture of fluids with fluids of different natures together, 

 or by dropping in salts or powders of different natures together into different 

 fluids : the two most common opposites, acids and alcalis, on being mixed, cause 

 a great ebullition or frothing, but no great heat ; but the solutions of some metals 

 in aquafortis cause intense heat, and emit flame : the mixing aromatic oils with 

 acid mineral spirits actually kindle, and burn with violent explosions ; and some 

 vegetable substances, putrifying with moisture, will sometimes heat so, as to 

 kindle what lies dry above that part of the heap where the putrefaction happens. 

 Thus dung heaps will heat, and haycocks often kindle into actual fire. 



In these cases' of effervescence, as there is no adventitious heat or fire applied, 

 there must be the elements of fire lying hid or dormant in one or other of the 

 bodies; and it is sufliciently known, by experiment, that there is abundance of 

 air lies dormant in all bodies both solid and fluid ; and it is likewise known, that 

 fire cannot exert itself without the elastic assistance of common air; for wood will 

 not burn, nor even gunpowder fire, in the artificial vacuum. It being therefore 

 granted, that there are the elements of fire and of air lying dormant in all bodies; 

 there is » iily required such an action as may set at liberty the particles of air and 



