1865.] Physics. 125 



The principle of carburetting coal gas has already been adopted 

 in other cases, but this method differs from all others hitherto in use 

 by the inventor employing naphthaline, and the heaviest hydro- 

 carbons, as the carburetting agents. These are placed in a gas-tight 

 metallic box, into which are soldered two gas-pipes, one for con- 

 veying gas into the box, and the other for conveying gas and vapour 

 out of the box into the burner. The burner is fixed to the outlet pipe, 

 and is so placed that when gas is being burnt, the hot air from the gas 

 flame must impinge upon the box. This box is provided with a screw- 

 plug through which the hydro-carbon is put in, and this plug is closed 

 during use. The box being supplied with hydro-carbon, or carbuline, 

 as the inventor styles the materials employed, is connected with any 

 ordinary gas-fitting, and the gas is lighted. At first the gas passes 

 over the surface of the hydro-carbon without being affected, but when 

 the temperature has risen sufficiently to convert the hydro-carbon into 

 vapour, the passing gas carries with it a quantity of this vapour, and 

 the flame becomes highly illuminating, the illumination being pro- 

 portional to the quantity of vapour present in the flame. As may be 

 imagined, the increase of light is enormous, as will be seen from the 

 following statement : — In London 1,000 feet of gas, costing 4s. 6d., 

 give the light of 1,500 candles, when burnt in flat flame-burners. An 

 addition to this of 4£ lbs. of carboline, costing about 9d., raises its 

 light to that of 7,500 candles. The apparatus is perfectly safe, and 

 gives no trouble. In some experiments made and verified by one of 

 our staff, it was. proved that the light given by gas passing through 

 the carburetter at the rate of three feet per hour, was eight times 

 greater than the light given by ordinary gas burnt under precisely 

 similar conditions, at the rate of three-and-a-half feet per hour. 



Some curious effects of the action of light upon some copper salts 

 have been noticed by M. Renault. When copper is plunged into any 

 liquid capable of abandoning chlorine more or less easily, it becomes 

 covered with a greyish white coating consisting of protochloride of 

 copper. This salt is remarkable for the facility with which it alters 

 when exposed to sunlight ; its greyish white colour gradually deepens 

 to black, and assumes a coppery metallic appearance. A photographic 

 negative placed on a copper plate rendered sensitive in this manner 

 gives a remarkably fine positive ; and when the coating of chloride is 

 sufficiently thin, the redness of the copper seen through the trans- 

 parent light parts gives a more agreeable tone than is possessed by the 

 old daguerreotype pictures. If the dry white crystalline protochloride 

 is spread on paper, and exposed to the sun, no alteration takes place 

 so long as the dry condition is maintained ; but on the addition of a 

 few drops of water, each portion of the moistened protochloride paper 

 assumes successively yellow, grey, black, and violet tints. The 

 analogy between the properties of chlorine, bromine, iodine, fluorine, 

 and cyanogen, led M. Renault to investigate whether analogous photo- 

 graphic compounds might not be furnished with those bodies. He 

 has accordingly obtained photographs with bromide, iodide, and 

 fluoride of copper, the bromide being considerably more sensitive than 

 either of the other compounds. In the early days of the daguerreotype 



