VOL. XLII.] PHILOSOPHICAL TRANSACTIONS. 567 



those pans, the liquor will penetrate that ferruginous place, and make a spot 

 there. By using earthen pans you will get a very limpid liquor, and which 

 will only have a very pale straw-colour, even after its perfect concentration. 



The lye prepared in iron, being kept for some time, clears up, and leaves a 

 black sediment, which is that part of the iron which it has separated by corrod- 

 ing the sides of the pot. And yet this ferruginous lye, together with the oil, 

 will form a white soap, if we let that black sediment precipitate. This sediment 

 is true iron. The Dr. has made himself sure of it, by calcining it in a crucible, 

 after having inoistened it with oil. 



One ounce of concentrated lye to the degree above mentioned, contains 3 

 drs. 18 grains of salt : when this salt is dissolved again in distilled rain water, 

 and filtrated, it yields 3 grains of coarse earth, which cannot penetrate the 

 pores of the filtre. 



To use it to make soap, take 1 part of it to 2 parts of the best oil : mix them 

 gently in a China bowl, stirring them with a spathula of white wood, till both 

 liquors are come to the consistence of butter that is churning : this thickening 

 is much sooner done in winter than in summer. Keep the vessel in a dry place, 

 that the moisture of the air may not diminish the strength of the lye. The mix- 

 ture daily grows to a body, and when it is in the sun in summer, and on the 

 chimney mantle in winter, the phlegm evaporating sooner, it becomes perfect 

 soap in 4 or 5 days, provided the lye be sufficiently concentrated. It will be 

 well however, that during the time the 1 liquors are binding together, the mix- 

 ture be stirred with the spathula, that the water may not be kept in, but evaporate 

 the sooner. When the soap is made, it easily comes out of the vessel, but it 

 has not yet lost all that moisture it should lose ; so that though it may be used 

 in that state, it is better to keep it 12 or 15 days longer ; at the end of which 

 time, if decompound, you always find the whole oil employed ; that is to say, 

 out of 18 drs. of this perfect soap, you get 14- oz. of oil, and 2 drs. 23 or 24 grs. 

 of salt of glass-wort. So after this method a patient may easily make his own 

 soap, and be sure of the ingredients ; perhaps even in the great manufactories, 

 one day or other, they may prefer this to that which is now in use. 



As to what relates to the oil of lime, (huile de chaux) spoken of in his experi- 

 ments, it is the caput mortuum of the sal ammoniac, after distillation of the 

 volatile spirit by means of quick-lime ; it is exposed in a fiat vessel to the 

 moisture of the cellar, whence a deliquiuin is formed, which is called oil of 

 lime. It is lime dissolved by means of the acid of the sea-salt, which is 

 contained in the sal ammoniac ; other chymists call it the fixed liquors 

 of sal ammoniac. Your soap-boilers are obliged to add sea-salt to their 

 soap, which probably comes from their making use of pot-ash in their 



