IS 15.] An Address to Chemists. \2f 



prepared oxalate of lead by pouring a solution of pure oxalic acid 

 into a solution of pure and neutral nitrate of lead. J did not era- 

 ploy acetate of lead, because that salt combines in part with all the 

 substances which precipitate from it, as 1 have shown in my expe- 

 riments on carbonate of lead, and more particularly in my Essay 

 on Organic Combinations. Oxalate of lead contains no water of 

 combination ; hence it is easily dried, and requires only to be 

 heated a few degi'ees above the temperature of the atmosphere. I 

 burnt it in a capsule of thin glass, of which I had exactly deter- 

 mined the weight. I heated it in the flame of a spirit lamp, 

 taking care to apply the first heat near the edge of the glass, and 

 advancing gradually to the centre. The oxalate takes fire and 

 burns quietly. When the whole is burnt I allow it to cool. 1 now 

 weigh the glass with the oxide which it contains. This oxide is 

 mixed with a small quantity of metallic lead, reduced by the char- 

 coal of the acid. I dissolve it in distilled vinegar, wash the residual 

 lead, dry it, and weigh it. To the weight of the oxide found, 1 

 add the quantity of oxygen requisite to convert the metallic lead 

 into oxide. By this method of experimenting, oxalate of lead 

 gave me 75'1(> per cent, of oxide of lead. I would not recom- 

 mend to the reader to repeat this experiment in metallic vessels, as 

 of platinum or iron. VVhen platinum vessels are used, I find that 

 nine times out of ten the reduced lead unites with tlie platinum 

 and spoils it. As to iron, every body knows that it increases in 

 weight in the fire. As to the water which I found in effloresced 

 oxalic acid, and to the difference between the result of the ana- 

 lyses of oxalate of lime, and of my analysis of oxalate of lead, 

 Mr. Dalton will^ive me leave to refer him to the experiments of 

 those, who in their analysis of oxalate of lime, have not neglected 

 the water of combination contained in that salt. 



Wlien I endeavoured to draw the attention of chemists to the 

 difficulties in the atomic theory, it was not my intention to refute 

 that hypothesis. I wanted to lay open all the difficulties of that 

 liyjjoihcsis, that nothing might escape our attention calculated to 

 throw light on the subject. I wished the experiments to verify the 

 theory ; and I should have considered it as absurd, if 1 had taken 

 the opposite road. I placed beside the corpuscular theory, a theory 

 of volumes ; because that theory is in some measure coimected 

 with facts which may be verified. To tliose who tliink that the 

 theory of volumes may be fatal to the corpuscular theory, I would 

 observe, that both are absolutely the same thing; but that the 

 tlieory of volumes has this immediate advantage over the other, 

 that it may l»e n)ore easily verified. I^et us sup|)ose for a moment, 

 that the theory of volumes were absolutely demonstrated. We 

 would then ask, what is the difference between a solid and a gaseous 

 body? The answer would restore to the corpuscular theory its 

 rights. It would be demonstrated i)y that of volumes. The only 

 difterence between the two theories consists in the words atom and 

 volume, that is to say, in the state of aggregation o( the elements. 



