296

CHLORIDE OF LIME.

expected to have benefited both the country and himself, by bringing home the earthy baseof that compound, at a moderate price; but was disappointed, to his cost.

Dr. Thomson is of opinion that the bleaching compound of lime and chlorine is not achloride of lime, but a combination of chlorous acid with lime and of chlorine with cal-cium ; consisting in its most concentrated state of

3 atoms of chloride of calcium = 211 atom of chlorite of lime - =11

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bo that about one third of the weight is chlorite of lime, to which alone the bleachingpowers of the substance are owing. He admits a fact, ratherinconsistent with this opin-ion, that bleaching powder does not attract moisture from the atmosphere with nearly somuch rapidity as might be expected from a mixture containing two thirds of its weightof so deliquescent a salt as muriate of lime; unless this indeed be prevented by the chlo-ride and chlorite being united into a double salt, which is a mere conjecture withouteither proof or analogy. And further, when dilute sulphuric or muriatic acid is pouredupon bleaching powder, a profusion of chlorine is given out immediately, which he alsoadmits to he inconsistent with the notion of its being a mixture of chloride of calcium andchlorite of lime, for no such evolution takes place when the above acids are mixed withsolutions of chloride of calcium and chlorate of potash. Though I am of opinion thatbleaching powder is simply a chloride of lime, in which the lime corresponds to the waterin the aqueous chlorine, yet I cannot see the truth or appositeness of his last reason, be-cause chlorine is certainly given out when chlorate of potash is acted upon by dilute mu-riatic acid, as any man may prove by adding to a mixture of these two substances a ve-getable color; for it will be speedily blanched. Dr. Thomson considers the chloride whichis at present made in Mr. Tennant’s great factory, as containing one atom of chlorine as-sociated with one atom of lime, or, taking his numbers, as consisting ofHydrate of lime 4-625Chlorine - 4*5

Or nearly equal weights of the chlorine and the base; indicating a surprising degree ofexcellence in the preparation. The average commercial samples of bleaching powderfrom different factories which I examined some years ago, did not possess nearly thatstrength; but varied in their quantity of chlorine from 20 to 28 per cent. In my synthe-tic experiments related above, the greatest quantity of chlorine that would combine withtlie atomic hydrate of lime, was in the proportion of 130 to 200 ; but there is no doubtthat if the lime contains additional water, it will condense more gas. I have never seena chloride of lime of the strength mentioned by Dr. Thomson, and I should think theremust be some fallacy in his statements. I have recorded in the paper above quoted anexperiment which proves that with additional moisture, a chloride of lime may be obtain-ed of the following composition : —

Chlorine 39*5Lime - 39*9Water - 20-61000

In the article Bleaching, of the Encyclopaedia Britannica, Dr. Thomson deduces fr® 10a test trial of Mr. Crum, that the best bleaching powder is a compound of 1 atom chlo-rite of lime = 11, 3 atoms chloride of calcium = 21, and 8 atoms of water = 9. 66adds he, “ in general the whole lime is not accurately saturated with chlorine. Accoringly 5 -when the bleaching powder is dissolved in water a small residue almost always remains undissolved. Unless the powder be fresh made, a portion of chlorite isconverted into chloride of calcium. It is probable therefore that the best bleaching p°der, as it comes into the hands of the bleachers, consists of1 atom chlorite of lime - 11

3 atoms chloride of calcium 216 atoms water - - 6*75

Impurity - - 2*25

41-00

• e If we consider the bleaching powder as a compound of chlorine and lime, our mode.j ecalculating will not be altered. Instead of 1 atom chlorite oflime, and 3 atoms cnof calcium, we shall have 4 atoms chloride of lime, 6 atoms water, and 2*25 of imp /as before. 53 In such ambiguity does this able chemist place this interesting jn

for theoretical reasons, of which I cannot see the value. Surely there is no dimeui^g jtconceiving chlorine to exercise a direct attractive force towards the hydrate of lime, ^is known to do towards each of its elementary constituents, the oxygen andSuch refinements as the preceding tend merely to mystify a plain matter.