80 PHILOSOPHICAL TRANSACTIONS. [aNNO 1786. 



dissolved the soap in hot water. When the liquor was cold, the soap floated at 

 top, the salt remaining in the water underneath. If too little salt was used, this 

 inconvenience did not happen, or not in so great a degree, though then less soap 

 was of course obtained. 



As diachylum, though with a greater proportion of litharge, and boiled longer 

 than that I had from the Hall, still contained oil not sufficiently saturated, I 

 made the metallic soap in another way. To a solution of sugar of lead in water 

 I added a solution of alkaline soap in the same liquid. A double decomposition 

 took place, the oil uniting with the calx of lead, the alkali with the acid of salt. 

 Using this metallic soap instead of the other, I obtained an alkaline soap harder 

 and more perfect than in the preceding process ; but still found that parts of the 

 oil remained with the calx of lead in the residuum, and adhered so firmly, that 

 repeated quantities of sea salt and spirit of wine did not wholly separate it. 



p. s. Since writing the above I have found, that if mild fixed alkali be added 

 to diachylum in hot water, they unite into a gelatinous mass, which is miscible 

 with the water. This may be considered as a kind of hepar. If this substance 

 be put into hot spirit of wine, the decomposition already described takes place. 

 If chalk be substituted for alkali, there is a similar result. I have found that 

 nitre is decomposed by diachylum in spirit of wine. I have also found, that if 

 the compound of diachylum and common salt be put into hot spirit of turpen- 

 tine, the diachylum is dissolved, but the salt remains at the bottom of the 

 vessel. 



Vll. An Account of some Minute British Shells, either not duly observed^ or 



totally unnoticed by Authors. By the Rev. John Lightfoot, M. A., F. R. S. 



p. 160. 



The shells which form the subject of this paper were discovered in the neigh- 

 bourhood of Bullstrode, in Buckinghamshire, by Mr. Agnew, gardiner to the 

 Duchess Dowager of Portland. The drawings of the shells were also made by 

 Mr. Agnew. 



The first-mentioned shell, a, pi. 2, named by Mr. Lightfoot Nautilus lacustris, 

 is of a flatted spiral figure, umbilicated on one side, convex on the other, but 

 slightly depressed in the centre, and measures about a quarter of an inch in dia- 

 meter: its volutes or spires are 4 in number: the mouth of the shell is obliquely 

 semioval, the upper edge projecting further than the lower: the substance of the 

 shell is very brittle and pellucid, and when recent is of a reddish brown or ches- 

 nut-colour, except 3 or 4 whitish curving streaks, from the centre to the circum- 

 ference, at nearly equal distances from each other. The internal structure of 

 this shell is extremely curious, the whole cavity being divided, according to the 



