286 



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 effloresce 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 redness, 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 -&?-& of the 

 quantity employed for saturation. The same experiment also gives 



f 62-5 

 the proportion of acid to base in the oxalate of lime to be < 3 7 '5; 



a proportion which differs from that of Bergman, because he neglect- 

 ed to neutralize the acid from which the lime was precipitated, 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 crystallizes 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 barely 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 pre- 

 ceding. Dr. Thomson having carefully examined, by direct satura- 

 tion 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 ox- 

 alate of strontian 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 strontian that had been contained in the former precipitate ; a 



