Dr. Uie on Chloride of Lime. 5 



hydrate of lime. It is very probable that the soluble combina- 

 tion is a neutral chloride, containing only half the lime of tlie 

 demi-chloride," M. Welter's instructions for the use of indigo, 

 as a test of bleaching-powder, are judicious, and shall be ad- 

 verted to afterwards. I do not believe in the truth of this ato- 

 mic partition, which M. Welter repeats after Mr. Dalton. I 

 find that 1 part of commercial chloride of lime, when well tri- 

 turated -with 19 parts of water, leaves a notable quantity of 

 chlorine in the undissolved part, while the solution does not 

 consist of an atomic chloride. 



More recently Dr. Thomson has published two papers on chlo- 

 ride of lime. The first seems to have been very hastily got up, 

 and is only remarkable for the employment of nitrate of silver, 

 to analyze a salt of commerce, which notoriously consists of 

 the chloride of lime and chloride of calcium ; and where the 

 great object is, to determine the proportion of each. Now, as 

 chloride of calcium, which is useless to the bleacher, yields 

 with nitrate of silver, a more abundant precipitate than chloride 

 of lime, it is evident that the worse the bleaching salt becomes, 

 the better it would appear to be, by Dr. Thomson's test. In 

 the same memoir * Dr. Thomson says, " Probably unslacked 

 lime might be united with chlorine, if its temperature could be 

 kept low." Now, in a paper which I published in his Annals 

 for September 1817, it is stated, that, when carbonic acid gas, 

 and chlorine, are subjected to dry quicklime at ordinary tem- 

 peratures, there is no condensation, but that they both unite 

 very readily with the calcareous hydrate t. In fact, when chlo- 

 rine is submitted to the hydrate, the temperature rises ; but 

 there is no heat produced on its admission to dry lime, because 

 there is no chemical action. 



Dr. Thomson's second dissertation is much more elaborate 

 than the first, displaying sounder views of analysis, and consi- 

 derable experimental address. The subject of this research was 

 a sample of bleaching-powder, manufactured at Belfast, and 

 which, he thought, had been modified by the carriage. " I 



* Annals of J'lal. Xlll., p. 185, lor Manli 1B19. t Idem, X., p. 213. 



