ALBUMEN. 341 



tube, if we would not injure the result of the whole analysis ; but 

 the circumstance that the substances must here be weighed on 

 filters (whose weight in a dry condition must be predetermined, 

 and which are, moreover, hygroscopic), and that the substances to 

 be weighed cannot be pulverised beforehand, very much increases 

 the difficulty of our forming accurate determinations. Animal 

 substances mostly form horn-like masses on heating, and become 

 covered during dessication by a crust of dry matter, which is 

 impervious to the water contained in the interior ; hence it is fre- 

 quently impossible to remove all the water contained in such sub- 

 stances without exposing them to a high temperature in vacuo and 

 employing sulphuric acid. We must therefore, when it is possible, 

 simultaneously employ high temperatures, air pumps, and hygro- 

 scopic bodies. As analytical chemistry indicates the numerous 

 methods in which these three agents for the removal of water may 

 be employed, we will here simply observe that the two following 

 methods appear to us % to constitute the most expeditious means of 

 attaining a perfect dessication. We either heat a small and con- 

 venient sand-bath under the receiver of the air-pump to about 

 110, and then place upon it the watch-glass or vessel on which 

 the substance to be dried, together with its filter, has already been 

 laid, and then place the sand-bath with the substance under the 

 air-pump over sulphuric acid, and form a vacuum ; or we place the 

 substance to be weighed, together with its filter, in a weighed test- 

 glass, which is surrounded by hot sand, and connected with a hand air- 

 pump provided with a chloride of calcium tube, and the air is then 

 abstracted exactly as in the manner directed by Liebig* in preparing 

 bodies for elementary analyses. In either case the dessication 

 should be continued as long as the substance is found to ex- 

 perience any loss of weight on being weighed. If the air-pump 

 be dispensed with, and the drying be conducted solely by means of 

 heat, as, for instance, by Rammelsberg's-f- or Liebig^sJ,' admirable 

 air-bath, the temperature must first be raised to 110 or 115, and 

 the substance then allowed to cool in vacuo, for if this precaution 

 were not adopted, the filter and the animal substance would, during 

 their cooling, abstract water from the air, and thus increase in 

 weight. The method proposed by Becquerel and Rodier for 

 weighing substances, while still hot, seems even less to be relied on ; 

 for it is well known that by the heating of one of the scales of the, 



* Handworterb. d. Chemie. Bd. I, S. 360. 

 t Anleit. zur quant, min. Analyse. S. 50. 

 % Anleit. zur quant, chem. Analyse. S. 37, 



