of Oxalic Acid and of Mercury. 1 67 



Being redissolved in distilled water, it was poured into the 

 oxalate of ammonia, and thoroughly mixed. When the li- 

 quid had become clear, a drop of it in a watch-glass became 

 turbid with muriate of lime. 0*89 grains of carbonate of lime, 

 treated as above, and gradually added, rendered the liquid 

 insensible to either muriate of lime or oxalic acid. A very small 

 additional portion of muriate made it answer to the latter. 



3rd. — 7| grains of the same acid, treated as above, with 

 6j grains carbonate of lime, the liquid was not affected by 

 either the acid or the muriate. A portion of it was poured off", 

 gently evaporated to dryness, and redissolved in a few drops 

 of distilled water. Oxalic acid was added to it, at intervals, 

 till the latter equalled the quantity of salt ; but the liquid con- 

 tinued pellucid throughout. 



4th. — An ounce of the same acid was re-crystallized, in a 

 solution as dilute as would readily form crystals. They were 

 still acicular, but firm and transparent. 9 grains treated as in 

 Experiment 2, with 6'25 grains of carbonate of lime, required 

 0*89 grains additional to throw down the acid. 



5th. — 9 grains of short firm prisms, which I had crystal- 

 lized three years ago, treated in the same w^ay with 6'25 grains 

 carbonate of lime, disappointed me, by still requiring 0"89 

 grains carbonate. In both these experiments exact satura- 

 tion was ascertained by concentration as in Experiment 3, 

 the tests being applied both before and after. 



In adoj)ting, therefore, 7g as the number for oxalic acid in 

 crystals, I do not mean any suspicion on Dr.Thonison's accu- 

 racy ; but suppose that our Northern brethren of oeconomical 

 renown have learned how to clear 12^ per cent on the cry- 

 stallization. 



With respect to mercury, as I do not think the case admits 

 of positive decision, probabilities are all we have to expect. 

 The inertness and dross-like aspect of the black oxide are 

 somewhat indicative of a suboxide ; calomel would seem to be 

 a subchloride ; and the protonitrate and salts precipitated from 

 it possess the characteristics of subsalts ; being very analogous 

 to those of copper, allowing for the difference of affinities and 

 of the consequent tendency to decompose acids and water. 

 Both are so classed by Ur.Wollaston and by 15erzelius. 



Oi" the pcrsalts of mercury, it does not appear in any che- 

 mical book I possess, that since the establishment of the ato- 

 mic theory they have undergone any examination on the plan 

 of compoiiiul (Iccotiipositioi), so admirably employed by Dr. 

 Thomson. They have been formed by ))ushing the solution 

 of tiiat metal, by heat, iu siil])liuric and nitric acids, as far as 



it 



