294 Gooch and Mar — Determination of Chlorine. 



A straightforward and easy method for determining the chlo- 

 rine is obviously desirable, and in the work of which we here 

 give an account we have endeavored to find such an one. 



It is a well-known fact* that when an aqueous solution of 

 hydrochloric acid is boiled a point of concentration is reached, 

 by the excessive loss of acid from stronger solutions and of 

 water from weaker ones, at which, for definite barometric 

 pressure, the liquid boils at a constant temperature and distils 

 unchanged in composition. It follows naturally that a degree 

 of dilution may be reached beyond which the loss of the acid 

 must be inappreciable. Indeed, Fleischer justifies his use 

 of hydrochloric acid as a standard in alkalimetric processes 

 upon his observation that decinormal solutions of this acid, 

 and even solutions of twice the strength (7*3 grms. to the 

 liter), do not yield after ten minutes' boiling enough acid to 

 redden blue litmus paper held in the steam. Hydriodic acid 

 behaves similarly to hydrochloric acid in the matter of volatil- 

 izing from aqueous solutions ; but to the decomposing action 

 of oxidizing agents it is far more sensitive. Our endeavor has 

 been to find conditions under which hydriodic acid may be 

 completely broken up, and its iodine removed from the solu- 

 tion by vaporization, while the hydrochloric is retained without 

 appreciable loss. As a first step toward the solution of this 

 question we initiated a series of experiments upon the volatility 

 of hydrochloric acid in solutions containing sulphuric acid, hav- 

 ing fixed upon the latter as the most available means of liber- 

 ating hydrochloric and hydriodic acids from their compounds 

 with the alkaline metals. After a few preliminary experiments 

 with litmus paper exposed in the steam from boiling solutions, 

 we settled down upon two modes of investigating this point. 

 According to the first, the determination of the chlorine re- 

 maining after concentration in solutions made up of water, 

 sulphuric acid, and known amounts of the chloride, by precip- 

 itating as silver chloride, filtering the precipitate on asbestos, 

 and weighing, was made the test of volatility of the hydro- 

 chloric acid ; in the second, the same object was accomplished 

 by estimating the chlorine escaping from the solution, by 

 passing the steam through a condenser and precipitating the 

 acid in the distillate by means of silver nitrate, collecting and 

 weighing the silver chloride as in the former method. 



The experiments of Series A to Series F were carried out 

 according to the first method. In them portions of a dilute 

 solution of potassium chloride of known value were measured 

 from a burette into Erlenmeyer flasks of 500 cm 3 capacity, 

 sulphuric acid diluted one-half was added, and the solution 

 was boiled until the flask and contents removed from the flame 



* Roscoe and Dittmar, Quart. Jour. Chem., xii, 128. 



