Art. LV.—Notes in Support of the Alleged Alkalinity of Carbonate of Line.
[Read before the Wellington Philosophical Society, 30th September, 1871.]
In a paper which appeared in the second volume of the Transactions of this Society,* I asserted the alkalinity of carbonate of lime, but the correctness of this assertion having been disputed by Mr. Charles R. C. Tichborne, F.C.S., of the Laboratory, Apothecaries Hall, Ireland, in a communication to the Editor of the “London Chemical News,”† I have re-investigated this subject and extended my researches upon it, by which I have arrived at results corroborative of the correctness of my statement, and which show besides that a large number of salts hitherto maintained to be neutral, or about which nothing has been affirmed, are in reality alkaline.
The latter results I will communicate in a separate form at an early date,‡ limiting myself in this paper to an attempt to clear the ground already broken, as far as I can, from the objections above referred to.
Mr. Tichborne very courteously, and with a considerable amount of plausibility, intimates that as the reddened litmus has the acid used to colour it only weakly combined with the tinctural matter of the paper, the carbonate of lime acts merely by absorbing this acid, and thus the litmus is brought back to its normal colour, blue with a shade of violet; and that therefore this is not a reliable test in such a case.
In answer to this I would ask, does not this capacity of the lime salt to abstract the acid, whether acetic or carbonic (for I guarded against encumbering the process with a double decomposition by using the latter acid), argue most forcibly and sufficiently for its alkalinity?
If it does not demonstrate alkalinity in such a case, then reddened litmus in opposition to all received opinion is not a proper test, nor indeed one at all, for ascertaining this character for any substance.
I would ask what other condition or property is required for a substance besides that enabling it to act as an alkali upon litmus, wanting which it is neutral?
[Footnote] * See Trans. N. Z. Inst., Vol. II., p. 150.
[Footnote] † See “Chemical News,” No. 565, September 23rd, 1870.
[Footnote] ‡ See Art. LVI.
However, I will not press this point further as I do not wish to rely upon one set of experiments, or upon any particular method I have adopted in them, for testing the truth of my allegation. I have therefore availed myself of the first test suggested by Mr. Tichborne for determining the question finally, and the results of this I will now describe.
Blue litmus paper after being well washed in distilled water free from ammonia till of a pale violet color, had its colour very distinctly changed to a deep blue on being pressed while moist upon a freshly fractured surface of calcspar. The failure of Mr. Tichborne to obtain a like result with this test I can only explain by supposing an omission on his part to insure a sufficiently large area of contact between the spar and the paper to render the chromatic change visible.
In regard to Mr. Tichborne's second test, I take exception to the employment of turmeric paper, as it only shows alkalinity in any substance in which it exists to a marked extent, and this is not a question of degree but one of condition—alkalinity or neutrality.
That turmeric paper cannot indicate alkalinity where this does not reach to a certain degree is manifest from the refusal of the organic base analine to affect it, although analine acts both upon reddened litmus and the juice of red cabbage as an alkali.
Again, I find pure strychnine, though it does not affect turmeric, behaves with reddened litmus just like an alkaline body, and this by the way may be a character of the alkaloids generally with such tests.
Lastly, to anticipate a little of the results of the investigation referred to, hydrous tribasic phosphate of lime does not colour turmeric, although we know, from the manner in which it may be produced and the circumstances attending its formation, that it must be alkaline, which character it plainly manifests to reddened litmus.
Thus we can mix alkaline solutions of chloride of calcium and tri-basic phosphate of soda, and the precipitate of phosphate of lime which falls leaves the supernatant solution distinctly acid. Now, as we have no reason for supposing that the phosphoric acid in changing bases has lost any portion of its combining or neutralizing power, we are constrained to hold that this precipitate is alkaline to an extent at least equally divergent from neutrality, as is the acid solution around it; and still turmeric paper does not indicate this alkalinity.
The turmeric paper test being therefore obviously unreliable for the detection of alkalinity in certain cases, I rely for the verification of the correctness of the statement in question upon the results of the first experiment suggested by Mr. Tichborne in the communication under review.
I have to apologise for allowing such a length of time to pass ere noticing
this criticism, but I waited in the hopes that some one might have taken up the question with such authority and potency of argument as would have settled it one way or the other, and thus saved me further thought on this subject, as it is so much more pleasant and exhilarating, besides being more in accordance with our colonial instincts, to break up fresh ground or explore new country, than to turn back from this to tinkering about old work, or to protect it from hostile blasts, even though these be ever so courteously blown or kindly tempered.
I will only add that I shall be very glad to have the subject still further discussed, especially as it now appears likely that some general principle may soon be recognised, by the use of which we can easily and certainly classify into the three distinctive groups, acidic, basic, and neutral, those bodies whose re-action with test paper is difficult to observe by reason of their intense colour or their extreme insolubility in water.