1820.] Physical Science dining the Year 18\9. 11 



water-trough. Expose the powder in a sandpot to a heat not 

 under 600° or 700°. A quantity of oxygen gas will be driven 

 off. Measure the bulk of this gas, and reduce it to what it 

 would be, supposing the barometer at 30 inches, and the ther- 

 mometer at 60°. Double this volume. It will indicate the 

 cubic inches of chlorine gas contained in 1000 grs. of the 

 bleaching powder. Turn this volume of chlorine into weight by 

 having recourse to the table of the specific gravities contained 

 in vol. iii. p. 25, of my System of Chemistry. Let this weight 



7 '25 



be = X. Then say, 4*5 : 7"25 :: x : -t:t-x = the weight of lime 



miited to the chlorine ; consequently the weight of subbichloride 

 of lime in the 1000 grs. of bleaching powder is equal to >r + 



7*25 ... 47 



-—• ^- Now this is equivalent to — - a . Therefore to find tha 



4*5 ^ 18 



weight of subbichloride of lime in the powder, we have only to 

 multiply the number x by 47, and divide the product by 18, or, 

 which comes to the same thing, we may multiply ,r by 2*61. 



It will be seen by inspecting the table of the constituents of 

 bleaching powder contained in my paper already alluded to, 

 that the quantity of muriate of lime contained in recently pre- 

 pared bleaching powder amounts to between 16 and 18 percent, 

 or about one-sixth of the weight of the powder. This portion of 

 muriate seems to be formed at the time that the chlorine unites 

 with the lime. Probably a small portion of muriatic acid gas is 

 mixed with the chlorine gas extricated from the mixture of 

 manganese, common salt, and sulphuric acid, in the stills ; at 

 least, I have always seen this the case when I myself prepared 

 chlorine gas in that manner. 



The water amounts likewise to about one-sixth of the weight 

 of the powder; so that the muriate of lime and water together 

 constitute about one-third of the powder. Not much less than 

 another third is uncombined lime ; so that the subbichloride of 

 lime' really contained in the bleaching powder, as it is usually 

 furnished to the bleachers, does not much exceed one-third of 

 the weight of the powder. 



It will be seen from another analysis contained in my paper, 

 that it is possible to make bleaching powder strong enough to 

 contain rather more than half its weight of subbichloride of lime, 

 and not more than five per cent, of uncombined lime. But I am 

 satisfied, from a great many trials, of the powder from various 

 manufactories, and from a careful inspection of the process, 

 that the manufacturer could not make the powder so strong upon 

 a large scale, except at a price that would render it useless to 

 the bleacher. 



o. Iodine. — Von Mons has described a pretty experiment with 

 iodine, which 1 have not repeated ; though I see no reason why 

 it should not succeed. The experiment is this: 



Dissolve some iodine in muriatic acid, and pour over the solu- 



