680 PHILOSOPHICAL TRANSACTIONS. [aNNO 17 AQ. 



The mechanism of the tempering of glass drops, applied to that of steel, is 

 the most simple of all the hypotheses, and answers all its properties, which are 

 these: 1. Tempered steel has a coarser grain. 2. It is increased in bulk. 3. It 

 is harder and brittler. 4. By annealing it becomes less brittle. 



Explanation: Steel made red-hot is filled and swelled, and its pores dilated, by 

 the igneous matter. In this state, the cold water, into which it is thrown, com- 

 presses and closes the parts of the surface, while the imprisoned igneous matter 

 dilates the pores within ; thus the texture of steel becomes more compact by 

 these two causes, while its pores are dilated. These large pores constitute the 

 coarse grain of tempered steel. Its dilatation by the igneous matter, which could 

 not be thoroughly condensed by the cold of the water, causes its augmented 

 bulk; the close texture of the substance that surrounds the pores, and the im- 

 prisoned igneous matter, occasion its hardness and brittleness. Its recoction or 

 annealing deprives it of this brittleness, and of a part of its hardness; because it 

 opens this texture, which it relaxes at the expence of the neighbouring pores, and 

 drives the igneous matter out of it. 



Also the fermentation of acids and alkalis seem to be another corollary of the 

 same principle. 



First, It is pretty universally allowed, that the acid particles have the figure 

 of small needles; and that alkalis are spheroidal or polyhedrous bodies, with a 

 vast number of pores proper to admit the acid needles. Secondly, Experience 

 shows, that salts are alkalised by fire, and that our juices are alkalised by heat, 

 &c. What can the repeated action of the fire produce on salts, in order to alkalise 

 them? it calcines them, blunts their points, and hollows them with avast number 

 of pores; and we see with the naked eye, that calcination has this effect on all 

 bodies. In short, it converts an angular very solid body into a very porous and 

 light spheroid; and this body is an alkali by the first supposition. Thirdly, cal- 

 cination introduces, and generally leaves in the pores of the calcined body, after 

 the operation, a great quantity of igneous matter. This matter is perceptible to 

 the senses in the lapis bononiensis, which becomes a phosphorus by calcination ; 

 in lime-stone, which by calcination is furnished with so great a quantity of igneous 

 matter, that in the effervescence, which is raised in it by throwing a little water 

 on this stone, you may kindle sulphur or a match by it. The alkaline, or alka- 

 lised salts also, that is, those that are calcined, have their pores full of the igneous 

 matter. Fourthly, such is the nature of the igneous matter, that it tears asunder 

 whatever opposes its passage, and makes it fly off with a report. This principle 

 is universally allowed: the effects of gunpowder, of volcanos and earthquakes, 

 prove it; and to come nearer our subject, unnealed glass breaks in the air, and 

 the lacryma Batavica does as much on breaking its small end. 



Whereas an alkali is a spongious body filled with the igneous matter, and an 



