508 PHILOSOPHICAL TRANSACTIONS. [aNNO I7OO. 



heat of the sun, and there remains behind tiiis urinous saU, whose taste is 

 something like sal ammoniac. 



At the Sulfatara, between Naples and Pozzuolo, they make alum in this 

 manner. In the summer they gather as nmch earth as they have occasion for, 

 which is there in the middle of a large area, and keep it in a dry place. After- 

 wards they put it in lead kettles of a good thickness, and pour upon it rain- 

 water; which is also impregnated with the same mineral. For which pur- 

 pose they take great care to dig some large pits, to preserve in them the 

 rain-water, which they carry to a large cistern near the kettles. They take 

 away the earth when the lixivium is made, and as it grows stronger by evapo- 

 ration, they put it from one kettle into another, till it is sufficiently evaporated. 

 They then take it out and convey it into a wooden tub, where after it is cooled 

 the alum sticks to the sides in the form of crystals. But the most remarkable 

 thing is, that these kettles are placed upon some of the great spiracula, where, 

 without any expence of fuel, only by the violent heat of these effluvia, the eva- 

 poration is constantly made sufficient for the crystallization. All this laboratory, 

 where the kettles, the cistern, with the tubs are, is only tiled over. The 

 governors of the great hospital of the Annunciata, who have been at the charge 

 of this ingenious contrivance, make now about 3 or 400 pounds a year 

 by it. 



As to sulphur : all summer long some labourers dig up and down in several 

 places of the same area, as in a kitchen garden ; by which means they give vent 

 to the copious sulphureous streams, that are within the bowels of all this moun- 

 tain : then out of the superficies of this earth, by the means of earthen pots, 

 they sublime the brimstone. 



For native sal ammoniacum: at the mouth of the largest spiracula, where 

 there is an excessive heat with a continual noise and smoke, is found a sort of 

 native sal amrnpniac : it seems the steams arise in a liquid form ; for if you put 

 in a key, a sword, or any thing solid, these effluvia will stick immediately to it 

 and drop down like water. All this mountain must be very full of mineral sub- 

 stances ; for when the effluvia are sublimed to the top of the spiracula, they 

 stick there to tiles or stones, where they form this salt, of which there is 

 gathered yearly about 200 pounds weight. It has much the taste of the 

 factitious sal ammoniac ; and, as a learned physician told me, being distilled 

 in a sand furnace, it yields a volatile urinous spirit, absolutely like sal ammo- 

 niac, both as to its sensible qualities and all other effects : he only observed 

 that the spirit had something aluminous in it ; to correct which, they added a 

 greater quantity of quicklime or salt of tartar, than in the distillation of the 

 common spirit. 



