928 



the author states that the lateral canals answer to the simple. Eusta- 

 chian tubes of Lizards and Mammals, and that the mediax canal, 

 with its dichotomous divisions, is a speciality peculiar to the Croco- 

 dilian reptiles. 



The memoir was illustrated by nine drawings of the size of nature. 



March 7, 1850. 



LIEUT.-COLONEL REID, R.E., Vice-President, in the Chair. 



A paper was read, entitled On the application of Carbon de- 

 posited in Gas Retorts as the negative plate in the Nitric Acid 

 Voltaic Battery." By Christopher Leefe Dresser, Esq. Commu- 

 nicated by Thomas Bell, Esq., Sec. R.S. &c. 



In the retorts used for the destructive distillation of coal to obtain 

 the carburetted hydrogen gas for the purposes of illumination, after 

 a certain time a deposition of carbonaceous matter takes place, and 

 which at length accumulates to such an extent as to fill up a portion 

 of the retort with solid substance, und to line the whole with a 

 coating varying from the thickness of paper to several inches. 



After describing several forms in which this substance occurs, 

 and which vary considerably both in density and hardness, the au- 

 thor states that he found one of great hardness, very little, if at all,- 

 porous, and of a stony fracture, to be best adapted for the negative 

 conductor of his nitric acid battery. The most convenient form for 

 the negative conductor is the prismatic, 1^ inch square on the side 

 and about 7 inches long, which is immersed 4 inches in the acid, 

 and used with round porous cells, the zinc cylinder being 3 inches 

 in diameter and 4?^ inches high. 



The carbon is cut into thin plates or prisms by the machine of 

 the marble cutter, at a cost of about l^d. each. The prisms may 

 be easily obtained 12, 14-, or 18 inches long. 



The only precautions necessary in using this form of carbon, are, 

 after using the plates to immerse them for a few moments in boiling 

 water, to take off the adhering acid, and then to dry them before a 

 fire or in a stove. 



Having used the same plates and prisms for months, the author 

 detected no deterioration of their conducting power, nor any de- 

 composition or alteration. The connexion was made by soldering 

 a strip of sheet copper to the zinc, and pressing this strongly against 

 the carbon with a clamp. 



Comparing these plates with plates of platinum, the author could 

 detect little difference in action, but the carbon appeared rather 

 superior. He states that his battery of 100 plates cost under £4, 

 whilst one of platinum of equal power Vv'ould have cost £60 or £70. 

 From the cheapness and durability of this substance, he considers 

 that it will make a valuable addition to our voltaic apparatus. 



