OF ARTS AND SCIENCES : JANUARY 31, 1866. 89 



experiment does not, therefore, prove that oxide of lead may not be 

 employed in this process with good results, when used for easily com- 

 bustible substances, and excessive heat is avoided. But it will, un- 

 questionably, be found preferable to use a substance which will give 

 directly a soluble chloride. 



Experiment 2. — This experiment was conducted as the last, with 

 only this difference, viz. that oxide of copper was substituted for 

 the oxide of lead. No better results, however, were obtained. The 

 reappearance of the difficultly volatile liquid in the vacant part of the 

 tube, while there was assurance of there being no deficiency in the 

 supply of oxygen, served to confirm the impression gained by the pre- 

 ceding experiment, — that chloroform could not be completely burnt in 

 oxygen alone, but that a substance having affinity for chlorine would 

 have to be mixed with the asbestos, at the point where the combustion 

 takes place. 



II. Experiments with Oxide of Zinc, mixed with the asbestos in the 

 posterior part of the combustion tube, as absorbent of Chlorine in 

 the analysis of substances difficultly combustible. 



As already indicated, the chief object of this set of experiments 

 was to determine whether the presence, at the point where combustion 

 takes place, of an oxide capable of combining with the chlorine would 

 have the effect to prevent the formation of the difficultly volatile liquid 

 above mentioned, and thus remedy that defect in the process. 



Experiment 1. — In this experiment, three grammes of oxide of zinc 

 were intimately mixed in a mortar with the quantity of asbestos neces- 

 sary to fill the space between a and b, Fig. 2, and that part of the tube 

 then packed with this mixture in the usual manner. A similar mix- 

 ture composed of asbestos and only one gramme of oxide of zinc was 

 placed between c and d. The space between b and c was still left va- 

 cant, in order to be able to observe the effect. On account of the vol- 

 atility of the chloride of zinc, it was deemed advisable to retain the 

 use of the air-bath to control the temperature of the anterior portion 

 of the combustion tube, which, in this experiment, was not allowed to 

 exceed 160° C. The result was, as anticipated, that no such conden- 

 sation of liquid between b and c occurred. In order to gain from this 

 experiment some idea of the degree of volatility of chloride of zinc 

 under such circumstances, the two columns of asbestos were treated for 



VOL. VII. 12 



