VOL. LXIX.] PHILOSOPHICAL TKANSACTIONS. 481 



hours together, tliat the friction between the grains of iron by this treatment 

 might break off such smaller parts as would remain suspended in the water for 

 some time : the obtaining of which very small particles in sufficient quantity 

 seemed to him to be one of the principal desiderata in the experiment. The 

 water being by this treatment rendered very muddy, he poured it into a clean 

 earthen vessel, leaving the filings behind ; and when the water had stood long 

 enough to become clear, he poured it out carefully, without disturbing such ot 

 the iron sediment as still remained, which now appeared reduced almost to im- 

 palpable powder. This powder was afterwards removed into another vessel, in 

 order to dry it ; but as he had not obtained a proper quantity of it by this first 

 step, he was obliged to repeat the process many times. 



Having at last procured enough of this very fine powder, the next thing to be 

 done was to make a paste of it, and that with some vehicle which would contain 

 a considerable quantity of the phlogistic principle ; for this purpose he had re- 

 course to linseed oil in preference to all other fluids. With these 2 ingredients 

 only he made a stiff' paste, taking particular care to knead it well before he 

 moulded it into convenient shapes. Sometimes, while the paste continued in 

 its soft state, he would put the impression of a seal on the several pieces ; one 

 of which is in the British Museum. This paste was then put upon wood, and 

 sometimes on tiles, in order to bake or dry it before a moderate fire, at about a 

 foot distance. The doctor found, that a moderate tire was most proper, because 

 a greater degree of heat made the composition frequently crack in many 

 places. 



The time required for the baking or drying of this paste was generally 5 or 6 

 hours, before it attained a sufficient degree of hardness. When that was done, 

 and the several baked pieces were become cold, he gave them their magnetic 

 virtue in any direction he pleased, by placing them between the extreme ends of 

 his large magazine of artificial magnets for a few seconds or more, as he saw 

 occasion. By this method the virtue they acquired was such, that when any 

 one of those pieces was held between 2 of his best ten guinea bars, with its 

 poles purposely inverted, it immediately of itself turned about to recover its 

 natural direction, which the force of those very powerful bars was not sufficient 

 to counteract. 



F'l. Account of an Extrnordinary Dropsical Case. By ]\Ir. John Latham, p. 54. 



Miss A. was of a florid, lively constitution, but from a child was subject to a 

 violent eruption, which came generally on a sudden, covering the whole neck, 

 breast, and often great part of the face ; and after remaining a week or 2 abated 

 in violence, and went off" by degrees. The intervals were uncertain, but for the 

 most part in spring and in autumn she was more apt to have it, though frequently 



VOL. XIV. 3 Q 



