OEGANIC COMPOUNDS CONTAINING BOEON. 
169 
beautiful green flame with which it burnt demonstrated the presence of boron as one of 
its constituents. 
In order to prepare this body in sutflcient quantity, several ounces of boracic ether 
were placed in a capacious flask closed by a doubly perforated cork. Through one of 
these perforations passed a thermometer, and through the other a short glass tube, one- 
fourth of an inch in diameter, and open at both ends: the bulb of the thermometer 
dipped into the boracic ether. Successive quantities of pure zincethyl were introduced 
through the short glass tube by means of a pipette, the elevation of temperature after 
each addition being allowed to subside before the next portion was added. The failure 
of a further addition of zincethyl to produce any rise of temperature was regarded as 
evidence of the completion of the reaction, which was not attained until a comparatively 
very large amount of zincethyl had been added. 
The liquid in the flask was now submitted to distillation in an oil-bath. It began to 
boil at 94° C., and between this temperature and 140° C. a considerable quantity of a 
colourless liquid distilled over. The distillation then suddenly stopped, and, to avoid 
secondary products of decomposition by the application of a greater heat, the operation 
was interrupted. On cooling, the materials remaining in the flask solidified to a mass 
of large crystals of ethylate of zinc and zincethyl. On rectification, the distillate began 
to boil at 70° C., but the thermometer rapidly rose to 95°, at which temperature the last 
two-thirds of the liquid passed over and were received apart. The product thus collected 
exhibited a constant boiling-point on redistillation. 
The combustion with oxide of copper of this liquid and the remaining boron com- 
pounds described in this paper presented some difficulties ; owing partly to the volatility 
of boracic acid in aqueous vapour, and partly to the tendency of that acid when fused 
to encase particles of carbon and prevent their oxidation. Fortunately the errors thus 
introduced were not so considerable as to throw any doubts upon the analytical results, 
although in many cases the excess in the percentage of hydrogen and the deficiency in 
that of carbon are somewhat greater than usual. To estimate the boron in the liquid 
obtained as above described, advantage was taken of the complete decomposition of the 
compound when heated to 100° with concentrated nitric acid in sealed tubes. The 
whole of the boron was in this way converted into boracic acid, but the latter could not 
be determined by the direct evaporation of the nitric acid solution, the loss of boracic 
acid amounting in such an operation to 15 or 20 per cent, of the whole amount. None 
of the known processes for estimating this acid appeared to be eligible in the present 
instance, and it therefore became necessary to seek for a new one. After the trial of 
various methods with but indifierent success, the following experiments showed that the 
evaporation of the acid solution of boracic acid with a known weight of magnesia in 
excess, the residue being then ignited, presented a process which, although far from 
rigidly accurate, could not, in the case of the boron compound to be analysed, diminish 
the amount of boron to a greater extent than about 0’2 per cent. 
MDCCCLXII. z 
