404 On the Definite Proportions in which the [Dkc. 



organic bodies, in hopes of rinding hereafter a suitable method- 

 Soon after the experiments of the French chemists came into my 

 possession, they suggested the idea of substituting hyper-oxymuriate 

 of potash for the brown oxide of lead. This method was attended 

 with success. I shall pass over my numerous unsuccessful trials 

 which led me by degrees to the method that I shall now describe. 



The substance to be examined must be obtained in a state of 

 purity, and quite free from water. It is frequently best to employ 

 it in a state of combination ; for example, with oxide of lead. It 

 is mixed in a mortar with five or six times its weight of hyper-oxy- 

 muriate of potash, previously reduced to powder, and strongly 

 heated. When perfectly mixed, nine or ten times their weight of 

 common salt, which has been recently melted in a platinum cru- 

 cible, is to be added, and the whole is to be well mixed. This 

 mixture is introduced into a glass tube, having a diameter between 

 a half and five-eighths of an inch, and sufficiently long to contain 

 the whole mixture. This tube (fig. 1, plate XXV.) is shut at 

 one of its extremities. A mixture of common salt with one or two 

 grains of hyper-oxymuriate of potash is first put into the tube, and 

 to fill about hall an inch of its lower extremity. Then the mixture 

 to be examined is introduced. I usually increase the proportion of 

 muriate of soda in the last quarter of the mixture, to have it more 

 in my power to moderate the combustion at its commencement. 

 What remains attached to the mortar is removed by means of 

 common salt in coarse powder. It is then put into the tube, and 

 the whole covered with a mixture of common salt and hyper-cxy- 

 muriate of potash ; so that the mixture containing the combustible 

 substance is included between two beds containing hyper-oxymu- 

 riate without any combustible matter. My reason for this is as 

 follows : The first effect of the heat decomposes the hyper-oxymu- 

 riate in the anterior part of the tube, and fills the tube with oxygen 

 gas; so that the decomposition of the combustible matter com- 

 mences in an atmosphere of oxygen. On the other hand, when 

 the decomposition is finished, the tube and vessels contain a mixture 

 of carbonic acid and oxygen erases. The last portion of the hyper- 

 oxvmuriate, the decomposition of which terminates the experiment, 

 gives out oxygen, which forces the carbonic acid gas out of the 

 vessels into the pneumatic trough, and this happens the more com- 

 pletely because the diameter of these vessels is too small to permit 

 the gases to mix. 



As to the shape of the tube, represented in fig. 1, I always make 

 it in the first place with a neck, through which I could introduce 

 the mixture ; and when this is done, I draw it out, by means of a 

 lamp, into the form represented in fig. 2. The intention of the 

 length of the neck was to be able to give it the shape of fig. 3, 

 without introducing into it any humidity produced by the flame of 

 the lamp with which the glass is heated ; and in order not to be 

 obliged to employ tubes unnecessarily long, I introduce the end of 

 the "tube, fig. 2, into a very small and thin glass represented of its 



