« VorigeDoorgaan »
In this series of structures, we have not only the gizzard becoming more and more fitted to economize the food as the country becomes less fertile, but we have also an extension of the lower intestines, and cæca, to such a degree as to lead to the belief that the processes carried on in them, render the undigested food subservient to the animal's support.
X. Additional Remarks on the State in which Alcohol erists in
fermented Liquors. By William Thomas Brande, Esq. F.R.S.
Read December 17, 1812.
he experiments and observations contained in this paper, are intended as supplementary to a communication on the same subject, which the Royal Society has done me the honour to insert in the Philosophical Transactions for the year 1811.*
On that occasion, I endeavoured to refute the commonly received opinion respecting the production of alcohol during the distillation of fermented liquors, by shewing, that the results of the process are not affected by a variation of temperature equal to twenty degrees of FAHRENHEIT's scale; that is, that a similar quantity of alcohol is afforded by distilling wine at 180° and at 200°.
I also conceived that any new arrangement of the ultimate elements of the wine, which could have given rise to the formation of alcohol, would have been attended with other
symptoms of decomposition, that carbon would have been deposited, or carbonic acid evolved, which in the experiments alluded to, was not the case. Upon such grounds I ventured to conclude, that the relative quantity of alcohol in wines, might be estimated by submitting them to a careful distillation, and by ascertaining the specific gravity of the distilled liquor with the precautions which I have formerly described.
* Page 337
This conclusion may be objected to, by supposing thaư the lowest temperature, at which the distillations were performed, was sufficient for the formation of alcohol from the elements existing in the wine; but it is not easy to conceive how this should happen, without some of those other changes which I have just noticed.
It has been stated, in my former paper, that the separation of alcohol from wine, by the addition of subcarbonate of potash, is prevented by the combination of the alkaline salt with the colouring-extractive, and acid contained in the liquor. I have also shortly noticed some unsuccessful attempts to separate these substances by other means than distillation.
In prosecuting the inquiry, this difficulty has been surmounted, and I shall proceed to shew, that alcohol may be separated from wine without the intervention of heat, and that the proportion thus afforded is equal to that yielded by distillation.
When the acetate, * or subacetatef of lead, or the subnitrate of tin I are added to wine, a dense insoluble precipitate is quickly formed, consisting of a combination of the metallic oxide, with the acid and colouring-extractive matter of the wine, and when this is separated by filtration, a colourless fluid is obtained, containing alcohol, water, and a portion of the acid of the metallic salt, provided the latter has not been added in excess, in which case a part remains undecomposed.
• Sugar of lead.
+ Formed by boiling two parts of sugar of lead with one of finely powdered litharge, in six parts of water. The solution should be preserved in well closed phials, as it is rapidly decomposed by attracting carbonic acid from the atmosphere. Even while hot, a poriton of carbonate of lead is formed in it. + Prepared by dissolving protoxide of tin in cold dilute nitric acid.
The acetate of lead and the subnitrate of tin produce the desired effect of separating the colouring and acid matters, in the greater number of instances, but they are less rapid and perfect in their action, and not so generally applicable as the subacetate of lead, * which is the substance that I commonly employed.
The following experiment was made with a view to ascertain the effect of this salt.
Twenty measures of alcohol, specific gravity ,82500, were mixed with eighty measures of distilled water coloured with log wood, and rendered slightly acid by supertartrate of potash. Four measures of a concentrated solution of the subacetate of lead were added to this mixture, and the whole poured upon a filter. A precipitate was thus collected of a deep purple colour, which appeared to consist of oxide of lead combined with tartaric acid and the colouring-extractive matter.
The filtered liquor was perfectly transparent and colourless, and afforded, on the addition of subcarbonate of potash, 19,5 measures of alcohol. +
• The effect of this salt upon colouring matter, was first pointed out to me by Mr. E. M. NOBLE of Chelsea.
+ Pure subcarbonate of potash, obtained by igniting the carbonate, was employed in these experiments. I found that about 19,5 parts of alcohol were separated in the course of four hours, by the addition of 50 parts of the subcarbonate to a mixture of 20 parts of alcohol by measure with 80 of distilled water, and that no further separation took place. The alcohol is always slightly alkaline, probably from containing a small portion of the solution of the subcarbonate, or of pure soda, but as this did not interfere with the object of the experiment, it was not particularly attended to.
When the subcarbonate was added to a mixture of four parts by measure of alcohol with 96 of water, no separation was effected.-A mixture containing 8 per cent. of alcohol afforded about 7 parts-one containing 16 per cent. about 15,5, and where the proportion of alcohol exceeded 16 per cent. the quantity, indicated by the action