CONSIDERED LIGHTER THAN WATER. 393 



water ; but I am not acquainted with any author who states the difference nu- 

 merically, excepting in the instance of biliary calculi, of that kind which is com- 

 posed almost entirely of this substance : GREN found the specific gravity of one 

 so low as .803. From the trials, I have made, it would appear, that the specific 

 gravity of cholesterine, in its pure state, is greater than that of water. Crystals 

 formed in alcohol on cooling, well washed with distilled water, are, I find, sus- 

 pended in a solution of salt of specific gravity 1.0102 at 50, and which, therefore, 

 may be considered as the specific gravity of the cholesterine itself. The apparent 

 greater lightness of biliary calculi formed of cholesterine, is clearly owing to the 

 air which they contain ; and to the same cause must be referred the circumstance, 

 that when crystals of this substance procured by the cooling of an alcoholic solu- 

 tion are thrown into water, most of them float, being buoyed up by the minute 

 air-bubbles disengaged on the admixture of the water and alcohol. If the crys- 

 tals are minutely examined, none will be seen to float excepting those to which 

 air-globules are adhering, and some of the larger size will be seen to sink, al- 

 though each of them may have attached to it a very minute air-globule.* 



Stearine, it is stated by M. RASP AIL, is of the specific gravity .795. From the 

 trials I have made on stearine, obtained from the suet of beef and of mutton by 

 boiling alcohol, I am disposed to infer, that, in its solid state, at ordinary tempera- 

 tures, its specific gravity differs but little from that of water. Alcohol, contain- 

 ing a sediment of stearine, which had separated and subsided on cooling, after 

 the addition of a portion of water purged of air, was submitted to the air-pump, 

 and was left under the exhausted receiver several hours without agitation. The 

 greater part of the stearine was found suspended midway ; a smaller portion had 

 reached the bottom, and a smaller still was at the surface. This admixture of 

 spirit and water was of specific gravity .98. Another mixture, which was turbid 

 throughout, from particles of stearine diffused through it, after rest of many hours 

 under the exhausted receiver, was of specific gravity .991. In this instance, there 

 was a thin stratum at the surface more opaque than the mixture generally, from 

 containing a larger quantity of stearine ; an excess which may have been owing 

 to the entanglement of a little air (for a small quantity was disengaged on ex- 

 haustion), or to those particles not being free from oleine ; or, it may be, they 

 contained included in them a little alcohol. In favour of this latter conjecture, it 

 may be mentioned, that when stearine, deposited from alcohol, has been a consider- 

 able time in water, its specific gravity seems to increase, its particles are carried up 

 and down in the ascending and descending currents of the fluid, or when these 



* Since the above was written, I find that Dr J. LAWRENCE SMITH, in a short article on Cholei- 

 terine, published in SILLIMAN'S Journal for January 1843, has pointed out the common error relative to 

 the specific gravity of this substance, but without endeavouring to determine it exactly. His conclusion 

 was drawn from finding it sink when fused and thrown into water. 



