492 PHILOSOPHICAL TRANSACTIONS. [anNO 170g. 



He observes, that tinctures made by digestion are usually very strong, and 

 saturated with the body whose tincture is extracted : but if the tincture be dis- 

 tilled in an alembic, the menstruum generally rises with its former colour and 

 clearness, leaving the body behind it : the reason of which he explains. 



He considers the several preparations of opium, and condemns such as are 

 made by the fumes of sulphur, or by acid liquors ; in which either the virtue « 

 of the opium is lost, by the evaporation of its volatile particles, or destroyed 

 by acid salts, whose qualities are directly opposite to that of opium ; the one 

 coagulating or making the blood viscid, whereas the other attenuates it, and 

 renders it fluid : but he approves of such preparations of opium as are made 

 with hot and aromatick medicines, which heighten its virtue ; and seems to 

 prefer Dr. Sydenham's preparation with canary wine to all others. 



Precipitation, he says, may be made by infusing a liquor, specifically lighter 

 or heavier than the menstruum : for by the first the equilibrium that was 

 between the gravity of the particles swimming in the menstruum, and the te- 

 nacity of the fluids, is destroyed, on which account they must sink. By the 

 second, the particles will be carried down to the bottom by the force of a 

 heavier fluid. He shows likewise, how precipitation may be caused by infusion 

 of saline menstruums, whose salts attracting the particles that swim in the 

 fluid, and cohering with them, they will form such bodies, whose gravity will 

 over-power the tenacity of the fluid, and descend. From which principle he 

 deduces the reason of all chemical coagulations.* 



In the crystallization of salts, he observes, that a great part of the fluid, in 

 which they are dissolved, is evaporated : on which account, their particles 

 coming nearer to one another, their attractive force is increased, and they will 

 come and unite together ; and because the figures of the minute particles of 

 each salt are always uniformly the same, and their attractions being stronger on 

 one side than another, they will always cohere to one another in such sides as 

 have the greatest attractive force. On which account they must necessarily 

 form bodies of certain determined figures, which in the same sort of particles 

 are always the same. 



JI, An Account of Animal Secretion^ the Quantity of Blood in the Human Body, 

 '^ and of Muscular Motion. By James Keill, M. D, N° 320, p. 324. 



The author of these discourses, in the preface, shows the necessity of a right 

 knowledge of the principles of true philosophy, and of the animal economy in 



* Dr. Freind had do just conception of elective attraction, nor of the nature of oaetallic precipi- 

 tates, &c. See his Life, vol. iv. p. 423 of this Abridgment. 



