Estimation of MolyMic Acid. 161 



20'='= of water and 20'='= of hydrochloric acid (sp. gr. 1-20) — the 

 same proportions as those used in the process of Friedheim 

 and Euler — were put into a 100'='= flask or narrow-based Erlen- 

 meyer, and boiled from a total volume of 40'='= to exactly 25'='=, a 

 point carefully marked on the flask. At this point of concen- 

 tration, tests, repeated in many cases, have shown no free 

 iodine in the reduced solution. If the solution 

 is boiled below 25'='=, there is a tendency for the 

 reducing action to go too far. 



The residue was diluted at once, neutralized 

 with acid sodium carbonate, and treated with an 

 excess of standard iodine. 



For a trap to prevent loss during boiling, a 

 two-bulbed calcium chloride tube, cut off as 

 shown in the figure four centimeters below the 

 larger bulb, was fitted loosely inside the neck 

 of the flask. Too violent boiling was prevented 

 by the addition of two or three small pieces of pumice stone. 

 While still acid the reduced solution, diluted and containing at 

 this time little hydriodic acid, is not appreciably reoxidized in 

 the air for some time ; but when once made alkaline, it is 

 very easily changed. Therefore the iodine for reoxidation 

 must either be added before the solution is made alkaline or 

 great care must be taken while neutralizing to stir the solution 

 as little as possible and to draw in the iodine immediately. 

 Less chance for error is introduced if the reduced solution is 

 put, with an excess amounting to at least 8'='= of decinormal 

 iodine and with a gram of tartaric acid, to prevent precipitation, 

 in a liter flask, corked and then neutralized with acid sodium car- 

 bonate. The flask was fitted with a paraffined rubber stopper, 

 carrying a funnel with a stop-cock for introducing the acid 

 sodium carbonate and a Will and Yarrentrapp trap for catch- 

 ing in a solution of potassium iodide any iodine thrown off 

 during the effervescence. In some of the test experiments 

 normal potassium carbonate, as causing less effervescence, was 

 substituted for the acid sodium carbonate during the first part 

 of the neutralization ; the solution, however, must always 

 finally be made alkaline with the acid carbonate. 



The simpler method of neutralization is to put the reduced 

 solution and a gram of tartaric acid in a liter flask, adding 

 enough sodium hydroxide to nearly neutralize the solution, 

 and finally making the solution surely alkaline with acid sodium 

 carbonate. An excess of the standard iodine must be drawn 

 in at once or atmospheric oxidation will take place and the 

 error of the process be great. 



If the solution has been properly neutralized according to 

 either method, the iodine color should perceptibly fade within 



