Chemical Science. 399 



known, and has described, as the result of his exertions, a new pro- 

 cess founded on the use of mercurial salts. Let muriatic acid be 

 added to a solution of protonitrate of mercury, in quantity more 

 than sufficient to precipitate all the mercury as calomel ; then let a 

 solution of chloride of lime be added : the chlorine set at liberty by 

 the excess of acid will react on the calomel, will convert it into cor- 

 rosive sublimate, which, dissolving, the solution will become per- 

 fectly clear and transparent again, if enough chloride of lime has 

 been added. 



This effect, when produced by known solutions of mercury and 

 bleaching powder, and with the attention required to obtain a com- 

 plete chemical action, is said by M. Marozeau to furnish a very 

 excellent method of ascertaining the strength of bleaching powder : 

 for by agitation of the liquids, all the calomel at first formed may 

 be converted into corrosive sublimate, and dissolved before the 

 slightest odour of chlorine is sensible in the residual liquor. He 

 uses the chlorometer of M. Gay Lussac, but inverts the office of 

 the pipette or fixed measure of bulk : instead of using it to measure 

 out the bulk of solution of chlorine to be tried, it is employed to 

 measure out a fixed quantity of the test solution of nitrate of mer- 

 cury, and the graduated jar is used to ascertain the quantity of 

 solution of chloride required to convert the calomel when formed into 

 corrosive sublimate. 



The strengths of the solutions of nitrate of mercury and bleaching 

 powder to be tried, are made to conform to the dimensions of the 

 instruments constituting Gay Lussac's chlorometer. The proof- 

 liquor is procured by boiling mercury in excess in dilute nitric acid, 

 continuing the ebullition until no deutonitrate remains in solution. 

 The strength is adjusted in two ways, either by preparing a solution 

 of chloride of lime with a known quantity of chlorine, and then 

 trying it against the test solution as yet unadjusted, and diluting the 

 latter until it agrees with this known solution, or by ascertaining 

 how much of the test liquor is required to precipitate the whole of 

 the chlorine in a known solution of common salt. For, as the 

 quantity of chlorine in common salt required to convert the mercury 

 in a given quantity of test solution into calomel, is exactly equal to 

 that required afterwards from chloride of lime to convert the calomel 

 so formed into corrosive sublimate, it is easy to make a known solu- 

 tion of salt, and to dilute the test liquor, until a given quantity of it 

 will exactly precipitate a measure of that saline solution ; and such 

 test liquor will, by the process recommended, show what quantity of 

 the solution of bleaching powder contains the same proportion of 

 chlorine as the standard solution of salt thus referred to. 



M. Marozeau then gives minute instructions for the use of this 

 process, intended for those who, not possessing much chemical 

 knowledge, still have to apply the instrument ; and he states that, 

 having used it very constantly, it has afforded him highly satis- 

 factory results *. 



* Ann. de Chim., xlvi. 400. 



