206 SOME REMARKS ON CLARIFICATION, ETC. 



in the above, yet I cannot agree with him for the reason that most 

 of the clarifying solutions act chemically as well as physically, in 

 consequence of which they must be carefully examined and used 

 accordingly. This is especially the case with chloral hydrate. Its 

 excellent double action, chemical and physical, and consequently 

 the ease with which it may be used, has rendered it a very desirable 

 clarifier. 



It is remarkable that as yet so little is known of the physical 

 properties and refractive power of the chloral hydrate solution. 

 According to my researches a solution of 8 parts c. p. crystallised 

 chloral hydrate in 5 parts of water has a specific gravity of i'3677 

 at 15*^ C. The refraction of sodium light is 1*4272, and the 

 divergence 0*0078. I have not been able to discover the refraction 

 of pure cellulose. 



If we consider, however, that pure cellulose is clarified almost 

 to invisibility in Canada balsam, while remaining clearly percep- 

 tible in glycerine of less and styrax of greater refractive power, we 

 may conclude that the refraction of cellulose is about that of 

 Canada balsam. The mean refraction of the latter is said by 

 Behrens to be i'535. 



There are a few drawbacks which must be mentioned in using 

 chloral hydrate as a clarifier. While the action of the alkaline 

 solutions may be nullified with acetic acid, and any turbidity 

 removed with ammonia, this is not the case wath chloral hydrate. 

 Fecula and almost the entire contents of the cells are more or less 

 dissolved by chloral hydrate and rendered transparent. In treating 

 these clarified objects with water or glycerine they become turbid. 



These defects are far less perceptible in a solution that I have 

 been using for the past six months, and which is composed of 

 equal parts of sodium salicylate and water. This solution has a 

 specific gravity of i'23i5 at a temperature of 17^ C. Refractive 

 power 1*4497 and divergence 0*01318 at 15*4° C. According to 

 my former observations the refractive power of the chloral hydrate 

 solution would equal that of a 67 per cent, solution of glycerine. 

 The salicylate solution, as I shall call my new liquid, shows a 

 refraction equal to that of a solution of 82 per cent, of anhydrous 

 glycerine. The penetrating power of my solution is greater than 

 that of chloral hydrate on account of its low specific gravity. Its 



