M. Caron on Cementation, 519 



tent3 of the tube as sulphuric acid, and is determined in the 

 usual way, with obvious analytical precautions. 



The applicability of this method was shown by the analysis of 

 bisulphide of carbon, of sulphite of ethyle, and of many other 

 sulphur compounds, and gave very satisfactory results. 



Some sulphur compounds by oxidation with nitric acid yield 

 the sulphur in the form of sulphurous acid. These are best de- 

 termined by fusion with nitrate of soda. 



With chlorinated bodies, a part of the chlorine is usually found 

 in the free state among the gases, and a modification of the 

 method is necessary. This consists in opening the tube under a 

 solution of sulphite of soda, by which the chlorine is absorbed 

 and immediately converted into hydrochloric acid, which is de- 

 termined in the usual manner. 



Bromine and iodine can also be estimated by this method, 

 which is further applicable to the case of metallic sulphides. The 

 analytical results were found in all cases to be very exact. 



The following experiments were undertaken by Caron* to 

 ascertain the nature of the process of cementation. 



An iron bar, completely surrounded by pieces of charcoal, was 

 packed in a porcelain tube which was placed in a reverberatory 

 furnace, and heated to redness, while pure hydrogen, carbonic 

 oxide, nitrogen, air, and carburetted hydrogen gases were passed 

 through the tube in successive operations, each lasting two hours. 

 In none of these cases was there any true cementation. 



With ammonia it was different ; after two hours' heating, the 

 bar was immediately tempered and hammered, and again tem- 

 pered, and then exhibited a regular and beautiful cementation of 

 ■£$ inch in depth. This was attributable to the action of am- 

 monia on carbon, forming at this temperature cyanide of ammo- 

 nium, which gives up carbon to the iron and forms steel. A 

 direct experiment was made, omitting the charcoal, and heating 

 an iron bar placed in a porcelain tube to redness in a current of 

 gaseous cyanide of ammonium. After two hours' heating, the 

 bar was treated as before, and was found quite cemented, espe- 

 cially at the end nearest the place at which the gas entered. 



It seemed probable that this property of cementation was not 

 confined to cyanide of ammonium, but was shared by other alka- 

 line cyanides : the cementation by means of yellow prussiate of 

 potash is probably of this kind. To decide this point experi- 

 mentally, the bar was placed in the tube surrounded by charcoal 

 impregnated with carbonate of potass, and heated to redness in a 

 current of air. Under these circumstances, as is well known, 

 cyanide of potassium is formed. After two hours the bar was 

 * Comptes Rendus, October 8, 1860. 



