447 



destroyed by the same cause as those which die from covering the 

 body with an impervious glaze ; for, in both cases, the conditions re- 

 quired for the access of oxidized, and, the removal of deoxidized 

 plasma, are wanting, and life necessarily ceases. The atmosphere of 

 unhealthy tropical climates differs but little from a vapour-bath at 

 a temperature of between 80° and 90° Fahr. ; and the dew-point in 

 those countries, as for example on the western coast of Africa, never 

 ranges lower than three or four degrees, nay, is sometimes only a 

 single degree, below the temperature of the air. Placed in an atmo- 

 sphere so nearly saturated with water, and of such a temperature, 

 man is on the verge of conditions that are incompatible with his ex- 

 istence : conditions which may easily be induced by exposure to fa- 

 tigue in a humid atmosphere under a burning sun, or other causes 

 which excite the skin while they prevent the exercise of its natural 

 function. The terms Miasma and Malaria may, according to the 

 author, be regarded as almost synonymous with air at the tempera- 

 ture of from 75° to 85° Fahr., and nearly saturated with moisture. 



2. A paper was also read, entitled, " On the Cause of the reduction 

 of Metals from solutions of their salts by the Voltaic circuit." By 

 Alfred Smee, Esq., F.R.S., Surgeon to the Bank of England. 



The reduction of a metal from its saline solution by the agency of 

 voltaic electricity, has, the author states, been explained in three 

 different ways. By Hisinger, by Berzelius, and by Faraday it has 

 been ascribed to the liberation of hydrogen in this process : Davy 

 and others considered it as resulting directly from the attraction of 

 the metal to the negative pole : and Daniell conceives that the metal 

 is directly electrolysed by the action of the voltaic circuit. The 

 a,uthor found that the ends of copper wires, placed in a solution of 

 sulphate of copper between two platina poles in the circuit, mani- 

 fest electric polarity ; so that while one end is dissolving, the other 

 is receiving deposits of copper : he also found that platina was, in 

 like manner, susceptible of polarity, although in a much less degree 

 than copper, when placed in similar circumstances. With a view to 

 determine the influence of nascent hydrogen in the voltaic reduc- 

 tion of metals, he impregnated pieces of coke and of porous char- 

 coal with hydrogen, by placing them, while in contact with a metal, 

 in an acid solution, when they thus constituted the negative pole of 

 the circuit ; and he found that the pieces thus charged readily re- 

 duced the metals of solutions into which they were immersed ; and 

 thence infers that the hydrogen is the agent in these reductions. 

 From another set of experiments he concludes, that during these de- 

 compositions, water is really formed at the negative pole ; a circum- 

 stance which he conceives is the chief source of the diflSculties ex- 

 perienced in electro-metallurgic operations when they are conducted 

 on a large scale, but which may be avoided by a particular mode of 

 arranging the elements of the circuit so as to ensure the uniform 

 diffusion of the salt. 



The author obtained the immediate reduction of gold, platina, 

 palladium, copper, silver and tin from their solutions by the agency 



