VOL. XLV.j PHILOSOPHICAL TRANSACTIONS. 577 



and taste; at least in any degree like what it has when made of the same potash 

 by a simple infusion in warm water. 



g. He evaporated some of the green lixivium, made only by infusion, and fil- 

 tred through a double rag: as soon as it began to boil, a green powder, to which 

 its colour is owing, fell to the bottom, and the lie became pale. After it was 

 evaporated to a pellicle, and set in a cool place, a salt separated from it on the 

 sides of the cup, in angular crystals like tartar. These crystals were soon 

 formed, and in pretty large quantities, but were difficult to separate from the 

 alkaline lie and salt, in which and the open air they were apt to dissolve : but 

 from the pellicle he obtained some pieces of the same salt that would not dissolve 

 in the open air. 



10. Oil of vitriol makes a strong effervescence with this green precipitate, 

 with a white fume, and a very strong sulphureous smell. It does the same with 

 these white crystals, though the sulphureous smell is not so strong. But with 

 the pure fixed alkali there was no such sulphureous smell to be discerned. 



From these experiments we may determine something about the nature and 

 contents of potash. This we are the better enabled to do, from the accurate expe- 

 riments and reasonings of the learned Mr. GeofFroy, on a like substance made 

 of charcoal and an alkali salt calcined together, in which he observed all the 

 properties and contents of potash above mentioned, particularly related in the 

 Memoirs of the Royal Academy, for the year 1717- This was made of the 

 same materials, and had all the properties above related of our potash ; particu- 

 larly a green lixivium, a strong sulphureous smell and taste, a sulphureous green 

 precipitate, crystallized salts, and sulphureous fumes with oil of vitriol. From 

 hence this learned author concludes, that this substance contained the active sul- 

 phureous parts of the wood, blended with more active igneous particles. These, 

 united with the alkaline salts, make a kind of soap, or sulphureous saponaceous 

 salt, resembling soap of tartar, or hepar sulphuris. The crystallized salts he 

 attributes to the acid of the wood, mixing with the alkaline salts. All these 

 parts of the wood then are contained in our potash ; and he observed the same 

 in the common soda, or cineres clavellati ; though they are in a less degree in 

 that, than in the Russian potash. 



Besides these, he shows that potash contains a metallic substance, which af- 

 fords the Prussian blue. We may add further, that the combination of these 

 principles makes many properties in potash, more than what result from them in 

 a state of separation. The most remarkable of these seems to be its explosive 

 quality ; which we take to proceed from the crystallized salts approaching to the 

 nature of nitre, and uniting with the sulphur and charcoal ; by which they form, 

 from all these ingredients of gunpowder, a kind of that ex losive substance, 



VOL. IX. 4 E 



