DR BROWN ON THE PRODUCTION OF SILICON FROM PARACYANOGEN. 245 



eible ; the chloride of potassium was removed by water, and the silicic acid left 

 anhydrous, undissolved, insoluble in boiling acids, decomposing fused carbonate of 

 potassa with effervescence, and forming by the last reaction either a deliquescent 

 salt or a dry glass, according as the proportion of potassa is greater or less. I 

 have sometimes found it necessary to repeat this twice, especially when working 

 with the ferrocyanide of potassium on the large scale. 



2. The same process was performed on the common ferrocyanide of potassium, 

 and with the very same result. 5.4 grs. of silicic acid were procured from 30 grs. 

 of the ferrocyanide of potassium. 



3. An iron crucible, in which the foregoing experiment had been made on a 

 large scale, was, in the interval between two operations with the ferrocyanide of 

 potassium, filled with carbonate of potassa, and heated to a full white heat for five 

 hours. The salt was then tested in vain for the presence of silicic acid. This ap- 

 pears to be a crucial experiment ; for, if it were possible that hammered iron 

 should contain silicon or silicic acid, and yield them up to the action of carbonate 

 of potassa with paracyanide of iron, in sufficient quantities to account for these 

 results, it should certainly, a fortiori, produce the same effects with potassa alone. 

 Besides, the same iron crucible was, in one instance, employed seven times succes- 

 sively, and no difference was observed in the several products. 



4. The same process was tried twice in a platinum crucible, with complete 

 success. 



5. The same experiment was performed on the ferrocyanide of potassium, 

 with the borate of soda instead of the carbonate of potassa. The product Avas 

 quite analogous to that which has just been described, with the important differ- 

 ence, that hydrochloric acid produced no effervescence of carbonic acid, a circum- 

 stance which illustrates the fact, that the carbon of the materials is not changed 

 into carbonic acid, even if such a supposition were allowable. In fine, as has been 

 once observed already, the disappearance of the carbon of the substances subject 

 to these operations, has to be considered and explained, as well as the prodiiction 

 of silica from them. 



6. During the last week, a crucible of the capacity of a pound and a half has 

 been worked seven times with 3334 grs., 2000 grs., and other similar quantities of 

 the ferrocyanide of potassium in succession. The products were all preserved ; 

 and, after ignition and purification, there were obtained 9334 grs. of silicic from 

 3240 grs. of ferrocyanide, although some of the product was lost in two of the 

 operations. The only purpose to be served by the notice of a rude experiment 



VOL xv. PART i. 3 u 



