168 Gooch and Kreider — Chlorine for Laboratory purposes. 



may be secured by wrapping the two lower chambers with 

 flexible metallic tubing through which steam is driven, or, 

 with equal convenience, by simply standing the whole appa- 

 ratus in heated water. When the simple precaution is taken 

 to heat the acid to 60° or 70° C. before allowing it to come 

 slowly into contact with the fused chlorate no difficulty what- 

 ever is met with in the practical automatic working of the 

 generator ; but if cold acid is permitted to act upon the chlo- 

 rate it becomes charged more or less with the chlorine dioxide 

 and a subsequent rise of temperature may cause dissociation of 

 the explosive gas with sufficient suddenness to expel the 

 liquid from the generator with considerable violence. The 

 gas evolved directly from the generator is never pure chlorine. 

 To determine the relative proportions of chlorine and chlorine 

 dioxide (the sole products of the action according to Pebal) 

 the gas as it issued from the generator was passed through two 

 pipettes fitted with glass stopcocks and joined to one another. 

 After allowing a reasonable time for the complete expulsion of 

 air from the pipettes the stopcocks were closed, and the 

 pipettes were disconnected from one another and from the 

 generator. The gas contained in one of the pipettes was 

 slowly forced by means of carbon dioxide through a solution 

 of potassium iodide ; that in the second pipette was driven 

 slowly by means of carbon dioxide through a hard glass tube 

 filled with asbestos and heated to redness by a Bunsen burner, 

 and then passed through a solution of potassium iodide. The 

 iodine set free in each case was determined in the acidified 

 solution by standard sodium thiosulphate, and the difference 

 in the amounts of iodine found was attributed to the action of 

 the oxygen of the chlorine dioxide. It was assumed that the 

 gas filling the pipettes ranged in line was homogeneously dis- 

 tributed, and this assumption is probably nearly enough true 

 for the purpose of this discussion. The temperature of the 

 acid in the generator was determined by inserting a thermom- 

 eter in the lowest chamber of the generator, so that the indica- 

 tion for the point of action is only approximate. 



In two experiments made with acid of half strength and at 

 indicated temperatures of 80° and 81° the chlorine in the gas 

 amounted to 81 - 6 per cent and 84 per cent respectively of the 

 mixture. A comparison experiment made with the strongest 

 acid heated to 50° — the highest temperature attainable without 

 evolution of the hydrochloric acid gas — the yield of chlorine 

 was 77"3 per cent. It is evident that the acid of half strength 

 acting at 80° is productive of a more favorable yield than the 

 strongest acid at 50°. 



Temperatures very much higher than those employed can 

 hardly be secured continually under the conditions of work, 



