Page:Proceedings of the Royal Society of London Vol 1.djvu/306

Rh we are indebted for the ﬁrst account of its properties. Dr. Thomson has in consequence undertaken a set of experiments, with the view of ascertaining various particulars respecting it.

Since the crystals of oxalic acid eﬂioresce and lose a part of their weight when moderately heated, he endeavours to ascertain what portion of this loss was to be ascribed to water of crystallization, by uniting a known quantity of the acid with lime, by precipitation from a known solution of it in muriatic acid.

The quantity of acid employed weighed 58-3 grains; the oxalate of lime produced, when perfectly dried, weighed 72 grains. This oxa- late being heated to retinas, gave 49'5 carbonate of lime; and by a further exposure to a violent heat, yielded 27 pure lime, which being deducted from 72 oxalate, left 45 for dry oxalic acid, or 11,1, of the quantity employed for saturation. The same experiment also gives the proportion of acid to base in the oxalate of lime to be 62'5 { 37‘5; 100'0 a proportion which dilfers from that of Bergman, because he lect- ed to neutralize the acid from which the lime was precipit, and which retained a part in solution.

To obviate any chance of error in so fundamental an experiment, Dr. Thomson thought it worth while to verify that analysis by a dif- ferent mode of operating. A known quantity of acid having been precipitated by lime-water, he obtained a quantity of oxalate of lime that corresponded accurately with the foregoing estimate.

The oxalate of magnesia is very similar to that of lime, and is not sensibly dissolved by water; nevertheless, if a solution of oxalate of ammonia be poured into a solution of sulphate of magnesia, no pre- cipitate is formed till after concentration by heat.

Oxalate of potash readily crystalline in ﬂat rhomboids, which dis- solve in thrice their weight of water at 60°. This salt also combines with excess of acid, forming a superoxalate, long known by the name of Salt of Sorrel, very sparingly soluble in water. The potash in this salt, as Dr. Thomson remarks, contains very nearly the double of that quantity of acid which would be necessary barer to neutralize it.

Soda also forms, with this acid, a salt that readily crystallizes, and it is said to be capable of combining with excess of acid; but Dr. Thomson has not tried it.

The oxalate of ammonia is much less soluble than either of the preceding. Dr. Thomson having carefully examined, by direct saturation of oxalic acid, the proportions in which the acid and base unite to form the several earthy and alkaline oxalates, gives tables of them, adapted to various practical purposes : but having remarked that oxalate of attention thus formed contained a larger quantity of the earth than was expected, he neutralized a known quantity of oxalic acid by ammonia, and with that compound made a precipitate from muriate of strontian. By this method of obtaining the compound, the same quantity of acid was found to have united with only half the quantity of stronﬁan that had been contained in the former precipitate ; a