186 ON CAST IRON. 



have escaped combustion ; but we must not forget, that very 

 small quantities of carbonate of lime are soluble in lime-water. 

 Si of this and Six inches ot this gas, and sixteen of oxigenized muriatic 

 16 of oxigeniz- gas were reduced in the space of an hour to half an inch, the 

 ed muriatic greater part of which was still oxigenized muriatic gas. A cloud 

 gas reduced by V ' i i • n • i f i i 



mixture to b was tormed at the instant ot mixture, and a light greasy pet- 



Greasv pellicle ^ c ^ e floated on the surface of the water, but I was not able to 



formed. examine it. This gas likewise contains phosphorus. Pbos- 



Containsphos- phorus, in fact, must occur in cast iron oftener than is ima- 



phoruG. gined ; for I have perceived a phosphate in almost all the 



solutions of our Spanish cast iron. But beside the ore there 



Phosphate in are some kinds of charcoal that contribute to this. That of 

 the ashes of .. ,.. , , , 



the quercus the evergreen oak, tor instance, must contain either phos- 



ilex> phorus or a phosphate, since the latter is found in its 



ashes. 



Their Plumbago. 



Carbon sepa- The carbon separated from cast iron has the leaden ap- 



rated from cast p earance lustre, and scaly texture of plumbago ; particularly 

 iron appears r J . . ' 



like plumbago, when it has been thoroughly freed from iron by the muriatic 



Is plumbago acid :' but is plumbago in fact a combination of iron with 

 a carburet . carbon, a metallic carburet, as it has been considered ever 

 since the time of Scheele ? His own experiments, in con- 

 junction with some particular facts, lead me to doubt this; 

 and I am at present fully persuaded, that, before we give im- 

 plicit credit to this combination, it would be proper to sub- 

 ject it to a fresh examination. 



Supcrcarburetted Cast Iron. 



Cast iron over- I had occasion to examine some cast iron that had been 



carbon by long renn£ d according to Grignon's principles, or by keeping it a 



fusion. l on g time in fusion. The cannons made of it were proved 



by the corps of artillery under the reign of Charles III, and 



would not stand the trials. 



This iron, when broken, had not the granulous appear- 

 and properties! ance °f g ra > r cast n ' on > ft exhibited to the eye a heap of small 

 needly cones, very obtuse, between which micaceous scales of 

 plumbago were visible when inspected with a lens. The 

 superabundance of this facilitated the crystallization. Under 

 the hammer it is compressed, and crumbles. The file cuts 



it 



