40 REPORT— 1839. 



The illustration of this general statement, and the exemplification of 

 the instance now cited by anticipation, were the objects of the author's 

 observations. 



While engaged in examining the visible properties of these dark, 

 opaque, and uncrystallized products of the decomposition by heat of 

 the cyanides and sulphocyanides of iron, copper, lead, zinc, bismuth, 

 silver, tin, and manganese, specified above, the author noticed on one 

 side of the field of the microscope a minute transparent fragment, 

 close in structure, refracting the light of the mirror peculiarly, and 

 trembling with uncommon brilliancy under the play of the illuminat- 

 ing lens. It was in that prepared from the sulphocyanide of copper. 

 The specimen was searched, and many more such clear morsels 

 found, some of them having even attempted a regular form. These 

 little crystals in all chemical respects conducted themselves in the 

 same manner as the amorphous powder among which they had been 

 found. 



Dr. Brown's experiments to determine on what their crystalline 

 structure depended, resulted in establishing the following formula : 



Formula. Let a parcel of any cyanide (or sulpho-cyanide) be care- 

 fully dried and put in a green glass tube, the open end of which is then to 

 be drawn out, and the attenuated part bent at right angles with the con- 

 taining. Immerse it horizontally in a shallow sand-bath suspended 

 over a spreading gas flame. Apply the heat with such caution as 

 shall secure that the whole apparatus be always as nearly as possible 

 at the same temperature at the same times. Let the flame be thus 

 progressively raised till the material in the tube has been brought to 

 that degree of temperature which may be called its point of decompo- 

 sition, which may be indicated in the case of a sulphocyanide by the 

 appearance of bisulphuret of carbon, and in that of a cyanide by the 

 impulse of liberated nitrogen on any light body held over the open 

 extremity of the tube. 



Whenever signs of decomposition have been observed, the flame 

 must be lowered as nearly as possible to that degree at which it is 

 able to communicate increments of heat equal to the decrements, by 

 radiation and conduction, of the apparatus. Continue the operation so 

 long as gas is extricated. In this way will the cyanide (or sulpho- 

 cyanide) have been decomposed, as nearly as manipulation can effect, 

 at its "point of decomposition"; the particles of resultant carburet will 

 have been slowly evolved one after another ; and, instead of throwing 

 themselves into a shapeless aggregation, will have affected the regu- 

 lated arrangement of crystallization. 



" 1st. Carburets thus crystallized are like sands of large grain ; the 

 granules having, many of them, regular forms, generally double octo- 

 hedrons. Larger crystals may be formed, although I do not know 

 how their formation may be secured. 



" 2nd. When prepared, they are opaline, or like semi-transparent 

 enamel. On being heated more strongly, they become perfectly 

 clear. I have heated them in the hottest blast of air and blast fur- 

 naces for hours without melting them ; without, indeed, producing 



