3 7 4 Mr. J. J. Hood on the Laws of Chemical Change. 



For the determination of the iron, a dilute solution of po- 

 fcassic permanganate was employed, the absolute strength of 

 which was never determined, as the experiments were wholly 

 relative. For the experiments made to find the influence of 

 temperature on the rate of change it was necessary to express 

 the different solutions of permanganate in terms of one stan- 

 dard, this being equivalent to using the same solution for all 

 the experiments. 



For measuring the solutions, 10-cubic-centim. and 50- 

 cubic-centim. burettes were employed ; the errors of calibra- 

 tion were so small that they were in every case neglected. 



Experiment 1. — There were taken 100 cubic centims. ferrous 

 sulphate solution containing '5772 gram ferrous iron with an 

 indefinite amount of hydric sulphate, 10 cubic centims. po- 

 tassic chlorate containing '2104 grm., and 200 cubic centims. 

 water : total volume 310 cubic centims. 



•5772 grm. iron is equivalent to '2105 grm. KC10 3 , by 

 the equation 



KC10 3 + 6 FeO = KC1 + 3 Fe 2 3 . 



All the solutions were immersed in the water-bath until 

 they had acquired the necessary temperature before mixing, 

 the iron solution being first run into the water, then the 

 potassic chlorate, and the whole well shaken. 



After standing in the bath five minutes, 10 cubic centims. 

 were withdrawn as rapidly as possible, run into a small flask 

 containing about 20 cubic centims. of water, to partially stop 

 the action going on by the dilution, and the remaining iron 

 determined by means of the permanganate, the whole opera- 

 tion occupying less than one minute. The time was always 

 noted just when the iron solution withdrawn had run out the 

 pipette. 



As an excess of permanganate had always to be added to 

 see the tint, "02 cubic centim. was deducted from the reading 

 of the burette for the coloration ; but in many cases no such 

 deduction was made. When the iron to be determined was 

 small, 20 or 30 cubic centims. were withdrawn for titration. 

 The following Table contains the results of this experiment : 

 the numbers under " permanganate calculated " are calculated 

 by theory from the observed times, and those under " time 

 calculated" from the permanganate found — the permanganate 

 found, or y, being the number of cubic centims. required for 

 10 cubic centims. of the experimental solution. 



Taking the first two observations to calculate the constants 



for y(a + t)=b 3 



we get a= 133-84, 6 = 1338-4. 



