1903.] 



Some Experiments in Magnetism. 



11 



This solution is used for the quantitative estimation of iron by 

 electrolysis, and though carbon is present in the oxalate, the deposited 

 iron is soluble in dilute hydrogen chloride, without any visible residue, 

 being pure to all chemical tests, but for possibly occluded hydrogen. 



Addenda : November 24, 1903. 



(1) . It should be stated that when the crystals growing in a 

 powerful magnetic field, and apparently orientated as described and 

 shown in the photograph, become large, and thus approach each 

 others' surfaces, they are often seen to leave their first position and 

 to take up another; sometimes the crystal will be moved bodily 

 nearer its neighbour, sometimes it is swung round only; but it 

 follows that where the crystals are numerous and close together, the 

 signs of orientation, which were evident during the early stages of 

 their growth, have almost, if not quite, disappeared at a later stage. 



(2) . Some experiments were carried out early in the investigation 

 in weak magnetic fields, and also in a field of as nearly zero intensity 

 as could be managed, by compensating the earth's field, but no 

 difference between these could be detected with any certainty, though 

 in most cases as many as six crystallisations were carried on at one 

 time, three in the strong field and three in a weak or zero field. 



(3) . When it was found that the direction in which the glass slides 

 used had been rubbed (before they were finally cleaned with acid, 

 alkali, and distilled water) was not in all cases negligible, experiments 

 were made in which the glass had been purposely rubbed hard in 

 different directions, with the result already stated, but in no case was 

 the orientation or arrangement of the crystals the same in appearance 

 as that shown in the photograph, for they formed close together along 

 the lines. The strongest argument, in the writer's opinion, against a 

 magnetic explanation of the orientation in the photograph, is his 

 repeated failure to obtain the same result under what were apparently 

 precisely similar circumstances, and also the fact that no other substance 

 has given similar indications, at any rate, such evident indications of 

 orientation, though very many have been tried. 



(4) . Since the paper was sent in, a number of experiments have 

 been made on the densities of the substances produced by " firing " 

 the small " squibs " of the mixtures of iron and sulphur described >in 

 the paper, with the results embodied in the following statement. The 

 quantities taken were in most cases between 4 and 2*5 grammes, and 

 the weighings were certainly correct to milligrammes ; the greatest 

 error possible in any single estimation of density does not exceed 

 ± 0*02, and is probably less than 0*005. All the bars fired in the 

 strong magnetic field are magnets, those in the earth's field are not 

 perceptibly so, though they may possess very weak polarity. 



