Scientific Intelligence. 171 



quantity of chlorine in any fluid, is found to be uncertain, or at least 

 incotwenient, on account of the variable quality of indigo, and also 

 of the changes of color which a dilute solution of indigo in sulphuric 

 acid spontaneously undergoes. If the solution be concentrated, the 

 sulphuric acid expels the chlorine too rapidly from its solution, and 

 thus prevents a portion of it from reacting on the indigo. Muriate 

 of manganese, proposed by A. Morin, is a more certain and prefer- 

 able test. He has been able to appreciate the half of a hundredth 

 parts of chlorine by this reagent, and nothing is more easy, he re- 

 marks, than to prepare it in determined proportions, and to preserve 

 it unaltered for a long time. To prepare this chlorometric fluid, it 

 is sufficient to dissolve some oxide of manganese in hydrochloric 

 acid, taking care to have an excess of the oxide. Filter the liquid, 

 which is of a pale rose color, and scarcely reddens litmus. A single 

 drop of a weak solution of sub-carbonate of soda, produces in it a 

 white precipitate, which does not disappear by agitation. These 

 characters indicate that the saturation is sufficient. In this state, the 

 solution of muriate of manganese is precipitated, of a deep brown, 

 by the chloride of lime ; the oxide being set free by the union of the 

 muriatic acid with the lime, which the chlorine kept in suspension. 

 It is obvious that, the solution of the chloride contains lime foreign to 

 its own composition, only in the state of muriate, of chlorate, or of 

 lime water. Now the muriate and chlorate of lime give no precipit- 

 ate with muriate of manganese ; lime water it is true yields a brown- 

 ish color but this proves to be of no importance, for on decomposing 

 muriate of manganese, by equal volumes of lime water and solution 

 of chloride reduced to 14°, more than 100 parts of hydrochlorate of 

 manganese were necessary for the chloride of lime, while less than 

 one part was sufficient for the lime water. 



The advantage which the solution of muriate of manganese offers 

 as a chlorometric substance, are threefold. 



1 . The uniform condition of the test. 



2. The disengagement of the chlorine is produced by an acid 

 which acts only while the metallic oxide, with which it is combined, 

 is precipitated. 



3. The precipitation of the oxide, which indicates the quantity of 

 chlorine, precedes the disengagement of the gas, or at most is simul- 

 taneous with it ; whereas in employing a solution of indigo, the chlo- 

 rine becomes at first free to react on the coloring matter, the destruc- 

 tion of which serves as the measure of its quantity. Hence the trial 



