420 Mr. J. J. Hood on Retardation 



way, by employing such salts as could not influence the oxi- 

 dation of the iron by any process of double decomposition. 



A solution (about 8 litres) of ferrous sulphate and hydric 

 sulphate was prepared from pure materials and preserved in a 

 large glass jar, arranged in such a way that any required 

 quantity of the solution could be siphoned off, while an atmo- 

 sphere of coal-gas was always maintained inside the jar. This 

 solution contained in 100 cubic centim. 



3-1416 grams ferrous iron, 

 •038 gram ferric iron, 

 11*84 grams free hydric sulphate. 

 The solution of potassic chlorate contained in 100 cubic centim. 

 1*933 gram. 10 cubic centim. being the amount required 

 to oxidize the iron in 16*86 cubic centim. of the ferrous 

 sulphate solution. The method of performing the experi- 

 ments was the same as has been already described in my 

 former papers. 



Each experimental solution consisted of 16*80 cubic cen- 

 tim. of the iron solution or -5296 gram Fe", and 1*996 gram 

 free H 2 S0 4 , together with the requisite amount of the salt 

 whose retarding effect was to be determined, the total volume 

 being made up to 250 cubic centim. with distilled water. 



The salts employed were purified from all traces of iron and 

 chlorides, dissolved in distilled water, and the strengths of the 

 solutions determined by double estimations of base and acid. 



The flasks containing the experimental solutions were placed 

 in a water-bath, usually six at one time, 10 cubic centim. of 

 the chlorate solution run into each, and the amount of oxida- 

 tion that had taken place after the lapse of various intervals 

 of time determined by permanganate. From two observa- 

 tions of the amount of unoxidized iron and time, the constants 

 in the equation y{a + t) = b were calculated, three minutes after 

 the addition of the chlorate being taken in every case as the 

 point £ = 0. 



As b in the above equation is inversely proportional to the 

 rate of change, or 



ty - _ V* 



dt~ b' 

 by a comparison of its values for a series of experiments, in 

 which other conditions being the same except the amount or 

 kind of salt added, with its value for a blank experiment, or 

 that in which no retarding agent is present, a measure of the 

 effect is obtained; these ratios multiplied by 100 are given in 

 Table II. 



To determine the equation for the blank as accurately as 

 possible, twenty-four experiments were made, in four batches 



