Dr. Ui e otl Chloride of Lime. 23 



tincture, according to the manner of proceeding, that is, ac- 

 cording as we pour the tincture on the aqueous chlorine, and 

 as we operate at different times, with considerable intervals ; if 

 the aqueous chlorine or chloride solution be concentrated, we 

 have the minimum of discoloration; if it be very weak, the 

 maximum. He says, that solution of indigo, containing about 

 Wos part, will give constant results to nearly JL^; and to 

 greater nicety still, if we dilute the chlorine solution, so that it 

 amounts to nearly one-half the volume of the tincture, which it 

 can discolour ; if we use the precaution to keep the solution of 

 chlorine and the tincture in two separate vessels ; and, finally, 

 to pour both together into a third vessel. We should, at the 

 same time, make a trial on another sample of chlorine whose 

 strength is known, in order to judge accurately of the hue. On 

 the whole, he considers that fourteen measures of gaseous 

 chlorine, can discolour 164 measures of the above indigo solution, 

 being a ratio of nearly one to twelve. The advantage of the 

 very dilute tincture obviously consists in this, that the excess 

 of water condenses the chlorine separated from combination 

 by the sulphuric acid, and confines its whole efficacy to the 

 liquor; whereas, from concentrated solutions, much of it 

 escapes into the atmosphere. Though I have made very nu- 

 merous experiments with the indigo test, yet I never could 

 obtain such consistency of result as M. Welter describes ; when 

 the blue colour begins to fade, a greenish hue appears, which 

 graduates into brownish-yellow by imperceptible shades. Hence 

 an error of -^^ may readily be allowed, and even more, with 

 ordinary observers. 



It now remains merely to determine the average state, and 

 equivalent weight, of the peroxide of manganese, so that the 

 manufacturer of bleaching powder, may be able to mix his in- 

 gredients in due proportion. My first experiments on this sub- 

 ject were calculated to shew the quantity of chlorine, evolved 

 from a certain weight of good commercial manganese, when 

 acted on by liquid muriatic acid in excess. The chlorine gas 

 was allowed to escape into the air, after passing through first a 

 little water, and then a tube filled with drymuriate of lime. 



