182 Miscellaneous Intelligence. 



lowing abridgment is from a paper of instructions how to ascer- 

 tain the value of this important bleaching agent, drawn up by M. 

 Gay-Lussac. The instructions are divided into two parts, the first 

 relates to the principle upon which the trial of strength is founded; the 

 second describes an instrument called a chlorometer, and the mode 

 of using it. 



It is known that chlorine has the power of destroying vegetable 

 colours ; and whether it be gaseous, dissolved in water, or united 

 to an alkali, the same quantity of chlorine will destroy the same 

 quantity of colouring matter. But as, when united to an alkali, it is 

 fixed, has scarcely any odour, is more readily preserved, is more fit 

 for carriage, and is much more concentrated ; it is evident that 

 this is the state which presents most advantages in its application. 



The combinations with potash, soda, and lime, are easily formed ; 

 the two first have been long Known in France under the name of 

 eau dejavelle; but in consequence of the re-action of the chlorine on 

 the alkalies and the production of inertbleaching compounds, when 

 concentrated, they can only be obtained in a very dilute state. The 

 third has been called oxymuriate of lime, but should be called 

 chloride of lime: it has not the inconveniences of the former, but 

 may be obtained, as is usual, in the solid form. 



As tisually prepared, it is, according to M. Welter, a hydrated 

 sub-chloride of lime, containing two proportions of lime, two of 

 water, and one of chlorine: when put into water it is decomposed, 

 half the lime precipitates, and the other half, combined with the 

 whole of the chlorine, remains in solution as a neutral compound. 

 The latter substance is very soluble, but may be obtained crystal- 

 lized in small prisms. The solution exposed to the air absorbs 

 carbonic acid, chalk precipitates, and the chlorine remains in solu- 

 tion; but excess of lime in the solution prevents this effect*. 



The mode of measuring the chlorine to which preference has been 

 giveii is that of M. Descroizilles, founded on the property which 

 chlorine has of destroying the colour of indigo. One of indigo 

 dissolved in nine of strong sulphuric acid and diluted with 990 of 

 ■water forms the usual test liquor. In similar circumstances the 

 chloride of lime discolours a quantity of test liquor proportionate to 

 its own ; but by varying the circumstances, the effect may be varied 

 also : for by pouring the chloride slowly into the test-liquor, much 

 more of the latter is discoloured than if it be poured slowly into 

 the chloride. The most constant effects are obtained by rapidly 

 pouring the one into the other, as to be afterwards described. 



As indigo varies, it is requisite in the first place to fix a standard 

 for it; and the unit of decolouring force has been taken, after 

 the example of M. Welter, from dry chlorine at the pressure 

 of 29.92 inches, and temperature of 32° Fah., the solution of 

 indigo being made of such strength as to have ten volumes dis- 



* See what Dr. Ure says on this subject, Quarterly Journal. 



