J 826.] to Dr. lire's Review, 1$ 



ciently near to be sure of the atomic composition of the salt 

 under examination. The application of sulphate of soda and 

 sulphuretted hydrogen is out of the question, because these 

 reagents would act upon the tartrate of lead in solution. Were 

 nitrate of lead to act indeed, as the author erroneously states, 

 the inference would be that the tartaric acid in the mixture was 

 in excess. 



In the analysis of tartrate of potash, I did not satisfy myself 

 with determining the quantity of tartaric acid in a given weight 

 of the salt, but ascertained likewise the amount of the potash. 

 My method was to ignite 16-5 grains of the crystals in a platinum 

 crucible, and to add to the solution nine grains of oxalic acid in 

 crj'stals. The potash was exactly saturated by this weight of 

 acid ; for the solution, after being heated to drive off the car- 

 bonic acid, did not alter the colour of litmus or cudbear paper. 



10. I do not know whether the remarks made by Dr. Ure 

 upon the non-precipitation of lead by sulphate of soda be in 

 jest or earnest. He would scarcely have hazarded them, I 

 think, unless he had reckoned rather too much upon my for- 

 bearance, and on the ignorance of the reader ; for so far as I 

 know it was I myself who first pointed out this remarkable fact 

 in a paper printed a good many years ago in the Aimah of 

 Fkilosophy. To advance a fact which I first pointed out as 

 a proof oif my ignorance of the value of the reagents which I 

 employed, is a degree of barefaced impudence to which every 

 chemist in Great Britain would have been unequal, except the 

 Andersonian Professor of Glasgow. 



1 1. There is one observation more of the reviewer to which it 

 will be requisite to attend before I conclude. He says that the 

 best way of obtaining pure salts is to take them as they are 

 prepared by manufacturing chemists. Were this recommenda- 

 tion to be adopted implicitly by young chemists, it would be 

 productive of most injurious mistakes. The competition in this 

 country among manufacturers is at present so great that they 

 are under the necessity of selhng at too low prices to be able to 

 produce their salts in a state of complete purity. Caustic potash 

 is always contaminated with lead. Muriate of barytes as it 

 comes from the makers is usually in the same predicament, and 

 unless it be purified will be unfit for use as a reagent. Nitrate 

 of silver always contains gold, often copper, and sometimes 

 potash.* Carbonate of soda always contains sulphuric acid. 

 Bicarbonate of potash is never free from lime. 1 have found 

 sulphate of lime in the magnesia of commerce ; carbonate of 

 zinc is a constant ingredient in acetate of zinc. Sulphate of 

 zinc is never, and sulphate of copper seldom free from iron. 

 Alum also is frequently contaminated with the same metal. 

 The muriatic acid of commerce is never free from sulphuric acid, 



* Last summer I was favoured with a specimen of this salt prepared for sale in 

 Dublin, which I found perfectly pure. 



