118 Prof. Regnault on the Specific Heat of some Simple Bodies. 



stals. I give in a note* the method of its preparation as de- 

 scribed by Captain Caron. 



M . . 



, . 87e r -62 



90^-12 



93^-07 



p. . . 



le r -6648 



1^-6648 



1^-6648 



T . . 



. 99°-40 



99°-81 



99°-20 



6' . . 



, . 22°-24 



21°-06 



19°-95 



Ad' . , 



, . 2°-8663 



3°-0303 



3°*1135 



A . . 



. 464s r -48 



464s r -48 



464» r -48 



C . . 



. 0-17811 



0-17986 



0-17818 



Mean .... 0*1787. 



I have therefore obtained for the specific heat of crystallized 

 silicon — 



* A mixture is made of — 



Dried silicofluoride of potassium .... 300 



Granulated zinc 400 



Sodium in small pieces 80 



These proportions are not absolutely necessary, but they seem to give the 

 best yield of silicon. The mixture thus made is projected into a crucible, 

 which, along with its cover, is red-hot. The reaction is brisk, although 

 when the cover is not sufficiently hot it is often necessary to press the mix- 

 ture with a clay pipe. When the whole is liquid, the crucible is removed and 

 allowed to cool. It is necessary to execute the operation as rapidly as pos- 

 sible, otherwise the crucible is liable to be perforated, and part of the zinc 

 and the silicon lost. 



The cooled crucible is broken to extract the ingot of zinc, which will 

 have settled down well if the operation has been successful : the crystal- 

 lized silicon is almost entirely at the upper part of the zinc. The pieces of 

 the crucible and scoriae adhering to the regulus are removed, and the latter 

 is melted at as low a temperature as possible, so that the zinc is liquid 

 while the silicon is solid. The zinc is run out and granulated, and can be 

 used for another operation : crystals of silicon remain in the crucible sur- 

 rounded by a little zinc. This residue is treated with concentrated hydro- 

 chloric acid, which removes zinc and iron, and crystallized silicon is left 

 still containing a little lead (if the zinc was not quite pure), and always a 

 little protoxide of silicon. The lead is removed by boiling with strong 

 nitric acid and washing, and the protoxide of silicon, as well as any of the 

 mass of the crucible, are removed by treatment with hydrofluosilicic acid. 

 The pure silicon which remains is washed with water and dried. 



To melt this silicon, it is mixed with silicofluoride of potassium and placed 

 in a double crucible, having been previously covered with a thick layer of 

 coarsely powdered glass. It is next heated to the melting-point of iron 

 for some time, and is then immersed while hot in cold water in order to 

 render the glass more friable. The crucible is then carefully broken, and 

 th? globule of silicon is found surrounded by glass, which is easily removed 

 either by a hammer or by means of a sharp-pointed steel. To purify it 

 completely, it must be boiled for some time with concentrated hydrofluoric 

 acid, which completely removes any slag, provided it is not in the centre of 

 the regulus. 



The only acid which attacks melted or crystallized silicon is nitrofluoric 

 acid. 



