and its relation to Ozone. 53 



trogen. The oxygen united with the elements of water separates 

 an equivalent of iodine from a solution of iodide of potassium, 

 like free chlorine or bromine. All that is now necessary is the 

 determination of this separated iodine, which may be effected 

 in the following manner with remarkable exactitude. 



A solution of iodine in iodide of potassium is prepared of such 

 a strength, that the liquid in one degree of the burette may con- 

 tain a small fraction of a milligramme, perhaps, as in the follow- 

 ing investigations 0*0002538 grm. of chemically pure iodine =a. 

 Some litres of extremely dilute sulphurous acid are also to be 

 prepared, to contain not more than T q 0% q o °^ sulphurous acid. 

 It must now be ascertained how many degrees of the burette t of 

 the solution of iodine are required to neutralize a measured volume 

 of this sulphurous acid. The quantity of iodine necessary is con- 

 sequently at. If the quantity n of this sulphurous acid be added 

 to the solution of iodine obtained by ozone, which contains the 

 unknown quantity of iodine x, this x neutralizes a portion of the 

 sulphurous acid. By ascertaining now the number of degrees 

 of the burette t 1 , and by this means also the quantity of iodine at' 

 which is necessary for the complete neutralization of the measure 

 n of sulphurous acid, the equation x + at' = nat, or x=a(nt—t l ) 

 is obtained. The point where the neutralization of the acid has 

 taken place may be readily determined by means of solutions of 

 starch, according to the process described by Dupasquier. From 

 x, or the quantity of iodine set free by the oxygen of the ozone, 

 we arrive at the equivalent quantity of oxygen, w, contained in 

 the ozone, together with the elements of water, by the readily 

 intelligible equation 



y 0(7^ — t') = w. 



As the entire weight of the ozone, less this oxygen w, consists 

 of water, it is only necessary now to determine this total weight. 

 This is effected simply by weighing a small globe apparatus, 

 through which strongly dried ozone is passed, and in which its 

 products of decomposition are retained in the solution of iodide 

 of potassium, and the water in a sulphuric acid tube attached. 



The following may serve as a proof of the accuracy of this 

 method. In the three following experiments the neutralization of 

 the same measure of sulphurous acid required the following 

 quantities of the diluted test-fluid, which only contained «= 

 0*0000.2538 grm. of iodide in a degree of the burette / : — 



t. at. Variation from the average. 



I. 122-9 0*003119 +0-000010 



II. 123-4 0*003137 -0000008 



III. 123*6 0*003132 -0*000003 



Average . . 0*003129 



