422 Prof. Magnus on the Origin of Tar in Olefiant Gas. 



M. Mitschcrlich indeed says, that, in order to prepare the gas 

 quickly and conveniently, it is well to make use of the original 

 method, and to four parts of sulphuric acid to add at once one 

 part of alcohol and then to warm cautiously ; I have found, 

 however, that the method according to which the alcohol is intro- 

 duced as vapour into the sulphuric acid, both as regards quick- 

 ness and purity of gas, is preferable to all others, and I have 

 therefore always followed this method. 



In order to free the gas from all wine-oil and aether, as also 

 from any trace of sulphurous acid that might be present, which, 

 however, was never observed, it was in the first place conducted 

 through several vessels containing concentrated sulphuric acid 

 and afterwards through caustic potash. In order to be certain 

 that no foreign gas was present, a small quantity of the gas was 

 collected over mercury, and fuming sulphuric acid allowed to act 

 on it. In some cases a quantity was collected over water, mixed 

 with chlorine, a specimen of which was completely absorbed by 

 caustic potash. After the Dutch oil had formed, caustic pot- 

 ash was added in order to take away the excess of chlorine 

 gas. Even when the olefiant gas prepared in this manner, and 

 recognized as pure, was heated to redness in a glass tube, the 

 production of tar was the consequence. 



It might be imagined, perhaps, that the gas still contained 

 slight traces of oxygen, as, according to the investigation of 

 Schrotter on the emission of light by phosphorus, traces of 

 oxygen are found in gases which have been purified in various 

 ways. To this, indeed, the pretty considerable quantity of tar 

 obtained could not be due ; but in order to be certain that the 

 tar is formed even when the gas is completely free from oxygen, 

 olefiant gas was conducted through a long glass tube, at one end 

 of which was placed a bit of phosphorus while the other end dipped 

 into mercury. After the gas had streamed through the tube for a 

 considerable time, and it might be assumed that all atmospheric 

 air was removed, the phosphorus was melted and the gas thus 

 freed from the least trace of oxygen. When the tube was heated 

 at a distance from the phosphorus, tar was immediately produced. 



In a similar manner a curved glass tube closed at one end was 

 filled with olefiant gas and the communication shut off with mer- 

 cury ; a portion of phosphorus was then brought into the bent por- 

 tion and there melted. The tube was then heated to redness at 

 another place, when the tar soon began to be condensed upon 

 the inside of the tube. It is therefore placed beyond doubt, that 

 tar is produced, even when olefiant gas, which is totally free from 

 oxygen, is exposed to a red heat, and that hence the tar can con- 

 tain nothing else than the constituents of this gas, namely, car- 

 bon and hydrogen. 



