1824.] M. Gay-Lussac on the Chloride of Lime. 223 



K. Another tube graduated like I, but in a contrary direction. 

 Its use is to hold the proof tincture which is to be poured 

 briskly into the chloride. For conveniently obtaining the de- 

 sired volume of the tincture, the tube L, drawn out to a point 

 at its lower end, is employed ; the excess of tincture is removed 

 by plunging the tube to the necessary depth into it, and closing 

 the upper orifice with the finger before it is withdrawn ; in the 

 same manner a deficiency may be supplied from the vessel con- 

 taining the indigo. 



Preparation of the Solution of Indigo, and of the Proof Tincture 



with that Solution. 



Take a determinate quantity of indigo, sifted through a silk 

 sieve, put it in a matrass with nine times its weight of con- 

 centrated sulphuric acid, and heat it in a water-bath, at the 

 temperature of boiling water, for six or eight hours. Dilute a 

 part of this solution with such a quantity of water that 1 volume of 

 chlorine may discharge the colour of exactly 10 volumes of the 

 solution : this will be the proof tincture. The simplest, and at 

 the same time sufficiently accurate method of preparing a liquid 

 containing its own volume of chlorine, is to take 3*98 gram. 

 of well crystallized manganese, and treat it with muriatic acid, 

 receiving the chlorine in milk of lime, whose volume is to be 

 reduced to that of 1 litre after the operation, as mentioned in 

 the assay of the oxides of manganese ; but if we wish to ope- 

 rate with the utmost accuracy, the chlorine must be prepared 

 in the state of gas, and absorbed by water in which a little 

 lime has been infused ; the temperature, pressure, and moisture 

 of the gas being noted. 



Important Observation. 



The proof tincture, being gradually discoloured by light, must 

 be carefully kept secluded from it in stone jars ; but for the use 

 of the chlorometer it may be preserved in a half litre glass phial, 

 always taking care not to expose it to the direct rays of the 

 sun : it had better be kept in a dark closet. 



Process of' Assaying the Chloride. 



Take several specimens from the mass of chloride to be exa- 

 mined, and weigh off 5 grammes, and pound them in the mor- 

 tar, with a sufficient quantity of water to make thin cream ; 

 then dilute it with more water, and decant it into the half-litre 

 jar. In order not to lose any liquid in this operation, rest the 

 edge of the motar against the pestle, as seen in the figure D. 

 Triturate the residual chloride remaining in the mortar with 

 water, and decant as before, and repeat these operations till no 

 more is left in the mortar. Rince it out and pour the rincings 



