334 Dr. T. Scheerer and Mr. W. Francis on some 



If we calculate the atomic relation for this combination in 

 the same manner as for the former, we obtain 



7'74 : 17-74, 



therefore exactly coinciding with that of the first combina- 

 tion. From the above-mentioned composition of the latter, 

 it appeared probable that the small quantity of sulphur in it 

 was combined with the likewise only small quantity of copper 

 forming the sulphuret of copper ; and that this was merely 

 mechanically mixed with the remainder of the combination. 

 This seemed to be the more admissible, as small quantities 

 of the sulphuret of copper often collect as slag (speise) on 

 the floor of the smalt-ovens at Modum*. The analysis of 

 the second combination proves, however, that copper and 

 sulphur do not stand in any relation, for here the quantity of 

 the first is increased to 8*90 per cent., while that of the latter 

 amounts merely to 0'50 per cent. 



With respect to the formula for the two combinations, it 

 must turn out to be the same for both, as the atomic rela- 

 tions 7 . 74 . . 17 . ?6 



and 7'74 : 17 '74 



approach so very near to each other. It is almost perfectly 

 coincident with the composition ascertained, if we adopt it at 



means of succinate of ammonia, the oxide of cobalt is obtained dissolved 

 in an ammoniacal fluid, from which it has to be precipitated by sulphuret 

 of ammonium. The filtration of the snlphuret of cobalt is, however, as 

 is well known, one of the least pleasant operations of analytic chemistry. 

 That the separation by my method sometimes proves unsuccessful, arises, 

 perhaps, not so much from the point of neutralization not being closely 

 enough attained, but rather, 1st, from the dilution after saturation not being 

 carried far enough ; or, 2ndly, from the solution not being sufficiently 

 stirred during saturation upon the addition of each fresh portion of caustic 

 potash ; or, 3rdly, from a potash being employed containing carbonic acid, 

 thus causing the fluid (from the carbonic acid dissolved therein) to act 

 acidly, even when the point of neutralization has been already exceeded. 

 Care must also be taken, that on the stirring round, no flocks of the oxide 

 of cobalt, which are precipitated at the first moment upon the addition of 

 the caustic potash, but soon redissolved, adhere to the margin of the 

 porcelain basin, and, drying upon it, escape solution. These, indeed, are 

 all circumstances which must be attended to, and which occasion some 

 difficulty in the employment of my method ; but which are easily over- 

 come by some practice. Whenever we shall be able to determine in ana- 

 lytic chemistry all bodies as easily and strictly as barytes and sulphuric 

 acid, then, indeed, such methods of separation as that just described will 

 become superfluous. SCH. 



* Nickel slag (Nickelspeise) does not occur here at all. SCH, 



