566 PHILOSOPHICAL TRANSACTIONS. [anNO 1/42. 



power. We may know also, that the lye has acquired the necessary degree of 

 concentration, when, becoming more active, we see, that the edge of the pot 

 that has been wetted by it, turns red, while the lower part of the side all around 

 down to the surface of the liquor, takes a greenish colour. Then the pot must 

 be taken from the fire, and the liquor left to cool so far as to be put into glass 

 bottles without cracking them : the bottles ought to be carefully corked, not 

 only to prevent the salts contracting a dampness from the air, which would 

 lessen the degree of forced concentration, which has been acquired by the eva- 

 poration, but also to preserve what is sulphureous, which would exhale, if the 

 liquor remained long exposed to the air ; for probably that sort of hepar, formed 

 by the union of the caustic salt with the sulphur of the ashes of the glass-wort, 

 ought not to be neglected. 



Now, the better to direct those who wish to work after these processes, and 

 to furnish them with the degrees of concentration this lye is to have, in order to 

 make with oil a solid soap out of it as speedily as possible, take a glass phial 

 with a narrow neck, and fill it with clear water up to a mark made on the neck. 

 That now used by the Dr. being filled up with water to that mark, contains 

 just 3 oz.: afterwards empty it carefully, and instead of clear water, fill it with 

 that concentrated lye as far as the foresaid mark, and then weigh it. If the 

 weight be increased 84- or 9 drs., that is, near 3 drs. in each ounce, this 

 shows that the lye is neither too much nor too little concentrated. An hydro- 

 statical balance, a water-poise, and other instruments, might also give this 

 degree ; but in the country they are not at hand, and he judged it best to 

 point out only what is most easy Soap-boilers use for this end a fresh egg ; 

 if one half of it sinks into the lye, they judge the latter to be of the first 

 strength, that is to say, that this is the lye which they ought to employ last 

 of all in their manufacture ; if the egg sinks in to 2 thirds, the lye is called 

 the second ; and, lastly, if the lye covers the whole surface of the egg, it 

 will be called the first, and will be that with which they begin their opera- 

 tion or boiling. But this way of trying has not all the exactness which can be 

 desired, because all hens' eggs have not the same specific gravity. Besides, 

 as he makes his soap without fire, he must take the lye that is most concen- 

 trated. 



Lest the iron, which is corroded by the lye, should enter into the composition 

 of the soap, we need only evaporate the lyes in earthen pans put over a balneum 

 mariae : but as this evaporation is slower, it will consume much more coals. 

 We may even see m tnose pans by different marks, that the liquor approaches 

 the desired degree of concentration, partly by a piece of wood marked with 

 notches, partly because if there is the least ferruginous speck in the earth of 



