40 PATTERSON AND FORSYTH : VELOCITY OF INTERACTION OF111.-The Velocity of Interaction of Iodic andSulphurous Acids in Variozcs Media.By THOMASTEWART PATTERSON and WILLIAM COLLINS FORSYTH.IN connexion with the experiments detailed in the preceding paper,we thought it would be of interest to examine some other type ofreaction, and chose, as one perhaps allowing of very simple observa-tion, the well kiiown experiment of Landolt on the reduction of iodica i d by sulphurous acid (Ber., 1886, 19, 1340; 1887, 20, 745).Dilute solutions of these reagents are mixed, a small quantity ofstarch solution being present, and after the lapse of a definite time,depending on the concentration of the solutions and the tempersture, a blue colour suddenly appears, due to the action of theliberated iodine on the starch.Landolt himself made some experi-ments regarding the influence of added inactive substances, andfound that acids-sulphuric, hydrochloric, oxttlic, acetic-hasten thereaction the more the greater is the afhity constant of the acid.Sodium chloride and ammonium chloride were also found to acceler-ate the reaction, but to a less extent. Similarly, alcohol in theproportion of 7 to 3 of water in the solution reduced the timenecessary for the appearance of the blue colour from 102.2 sea. to90.4 secs. He says that the influence of alcohol is thus not great,and that he was unable to find a liquid which definitely retardedthe velocity of the reaction.For the following experiments oar reagents were made asfollows: Of a saturated solution of sulphur dioxide, 50 C.C.werediluted to a litre, whilst 10 grams of iodic a i d were dissolved in1 litre of water. For an experiment, 10 C.C. of sulphur dioxidesolution were first mixed with 2 C.C. starch solution, and to thiswere added 106 C.C. of diluent, water, for example. To thismixture 10 C.C. of iodic acid solution were quickly added, thetemperature being about ZOO in all cases. In the above instancethe blue cdour flashed out in nineteen seconds. In other experi-ments, instead of the 100 C.C. of water, 100 C.C. of pure methyl,ethyl, n-propyl alcohol, or acetone, or mixtures of these with waterxn known proportiom were added. The colour which appeared inthe solution was blue or yellow, according to the proportion ofneutral solvent added.In the case of methyl alcohol the following r e d & were obtained:Percentage of methyl alcoholin 100 C.C.of added diluent. Time.0 19 seconds50 9 7 7100 .z 9IODIC AND SULPHUROUS ACIDS IN VARIOUS MEDIA. 41It thus appears that the addition of methyl alcohol hastens thisreaction very considerably, and practically in direct proportion tothe quantity of alcohol added. It was then found that ethyl andn-propyl alcohol behaved in a manner quite similar to methylalcohol, the accuracy of the method of investigation being insuffi-cient to detect any distinct variation.On the additioa of acetone the results were somewhat different,as the following table shows :Percentage of acetonein 100 C.C.of added diluent. Time.25 23 ¶ *50 24 Y Y75 15 ))100 3 9 )0 19 seconds60 2o Y JThe velocity of tho reaction increases at first as the proportion ofacetone increases up to about 50 per cent., todiminish again rapidlythereafter.It is not possible much to extend the examination of this reaction,since the scriveiits used must (1) be neutral or acid, and (2) bemiscible with water, two conditions which considerably limit thenumber of available liquids. In addition, although the reaction isone which can be timed fairly accurately, the variation in colour ofthe starch iodide and also the complexity of the whole reactionrender the results at least difficult of interpretation.We need only remark that an increase in the velocity of areaction, on the addition of a neutral solvent, to reach a maximumhas been observed in numerous cases; thus, Dawsm (Trans., 1911,99, 1) found the reaction between iodine and acetone with a littlesulphuric acid in presence of ethyl alcohol t o be very greatly reducedby the addition of small quantities of water, whilst Tubandt(Annalen, 1907, 354, 259) has recorded a somewhat similarobservation in regard to the inversion of menthone. For otherreferences Dawson’s paper should be consulted.ORGANIC CHEMISTRY DEPARTMENT,UNIVERSITY OF GLASGOW