264 
MESSRS. W. N. HARTLEY AND A. K. HUNTINGTON ON THE ACTION 
Specimen No. 2.—Another sample similar to No. 1, obtained from Messrs. Hopkix 
and Williams. 
Specimen No. 3.—Prepared by us from a beautifully crystallised specimen of 
formiate of lead, by decomposing the salt, after drying it at 130° C., in a current of pure 
dry sulphuretted hydrogen, and subsequent distillation from a further quantity of 
formiate of lead crystals. 
Specimen No. 4.— Consisted of two or three portions of the acid fractionally distilled 
during the preparation of the substance from oxalic acid and glycerin. 
All these specimens were manifestly impure, for they yielded spectra in which the 
more refrangible rays w 7 ere absorbed to a varying extent in every case, the absorption 
being considerable. The acid prepared from the lead salt by means of sulphuretted 
hydrogen gives the shortest spectrum and probably contains some sulphur compound. 
We have been much troubled by repeated attempts to prepare pure formic acid. It 
was decided, if possible, to oxidise pure methylic alcohol to the acid. When bichromate 
of potash and sulphuric acid are used for the purpose there is a danger of oxidising the 
acid to carbonic acid ; and when we consider, too, that in order to oxidise 16 grammes of 
alcohol a litre of a solution of the bichromate salt is required, it is easily seen that the 
formic acid will be diluted so largely that in the process of separation by distillation 
the product would be destroyed—at any rate this method was unsuccessful. The 
action of sulphuric acid and manganic oxide or tartaric acid does not yield a pure 
substance. The action of oxalic acid on formiate of barium yields a distillate which at 
first is different from the product of other processes in being free from a slight but 
peculiar odour, and which it is highly probable is not proper to formic acid, but belongs 
to* some ever present impurity. On continuing the distillation, the usual smell was 
developed, which fact seems to show that heat causes a change in the formic acid. It 
is said by Lomn ( vide AVatts’ ‘ Dictionary of Chemistry,’ vol. vi.) that formic acid 
of 87 per cent, can be obtained by the dry distillation of cupric formate. It is quite 
true that a small quantity of very weak formic acid can be obtained by this process, 
but as soon as all the crystalline water has been distilled off no yield of formic acid is 
obtainable from the salt. The products of the action of heat on the dried salt when 
maintained at a temperature of 200° in a paraffin bath, are metallic copper, carbonic 
acid and water, and, in all probability, carbon monoxide is formed. 
The specimens of formic acid examined by Dr. Miller and by M. Soret give much 
shorter spectra than ours. The formic acid examined by the latter observer absorbed 
all the rays beyond the 8th cadmium line, while the two better of our specimens 
transmit rays to a distance midway between the 12th and 17th lines (see Diagram 2), 
and that too through double the thickness of liquid. 
Acetic Acid. —Two or three specimens of the glacial acetic acid of commerce were 
examined, as w T ell as specimens carefully purified by distillation and crystallisation. 
The spectra were the same in each case, transmitting rays just beyond 17. 
