578 PHILOSOPHICAL TRANSACTIONS. [aNNO 1748. 



whose parts are highly rarefied in an intense and confined heat, by which they 

 readily explode in boiling lie. 



By this we may perceive, that the difficulty in making potash aright, is, first 

 to reduce the materials to cinders and ashes, and at the same time to preserve 

 their volatile, sulphureous, and exhalable acid parts, that are totally destroyed 

 in such a degree of heat ; and secondly, to calcine these ashes still further, so as 

 to flux their salts, and vitrify their terrestrial parts, and at the same time to keep 

 them separate from each other, or prevent their running into an indissolvable 

 glass. To give potash some of these properties, seems plainly to require a degree 

 of heat that will totally deprive it of others. 



The most likely way by which it comes to receive all these properties, is fi*om 

 the way of making it in Sweden above described. In that process, the green 

 fir, in which the ashes are burnt, impregnates them with the acid saline parts of 

 the wood or tar, which is well known to be in pretty large quantities, and is ab- 

 sorbed and fixed by the alkaline salts, and porous terrestrial parts of the ashes in 

 this process ; so that, besides the fixed alkaline salts of the ashes, the potash, 

 thus made, must likewise contain the more volatile salts of the pine, which are 

 exhaled in smoke by burning the pine alone in the open air. Besides these, it 

 likewise contains the resinous parts and sulphureous fumes of the pine, that are 

 hindered from exhaling by the heap of the mass. 



At the same time the alkaline salts are fluxed in the open fire, and in a manner 

 vitrified with the terrestrial parts of the ashes, which gives them their hard and 

 solid consistence; while the sulphureous and acid parts of the green wood hinder 

 them from turning to a perfect glass, or inert calx. All these parts united to- 

 gether in the fire, make that saponaceous substance we find in the potash thus 

 made, which further hinders the vitrification of the mass, and endows it with 

 ipany of its most peculiar and active properties. 



.. From hence we may see how difficult it is to make a substance endowed with 

 all these properties in any other manner. This is the reason why we could never 

 before make potash equal to that of Russia, and the other northern countries, 

 though we have much greater plenty of materials and perhaps better : for this 

 wav of making it has never before been thought of by the learned, or practised 

 any where else, as far as known. 



Somewhat of the same qualities are communicated to the English potash, by 

 the way of making it above described ; but in a degree as much inferior, as dry 

 straw, used for that purpose, is to green wood : accordingly our workmen find 

 that potash as much inferior to the foreign, for many purposes. 



From this account of the contents and qualities of potash, and the way of 

 making it, we may form some judgment of the other ways of making it, pro- 



