INTENSITY OF MAGNETIC AND DIAMAGNETIC FORCES. 7^7 



that described in paragraph 5, the force with which the mass in 

 each case, when exposed to the two half keepers, was attracted 

 by them, was determined. To excite the magnetism in the large 

 electro-magnet, six platinum elements were used ; the exciting 

 liquid consisted of commercial nitric acid, and of sulphuric acid, 

 the latter being diluted in the proportion of 1 : 12 according 

 to volume *. The intensity of the current during the continuance 

 of the experiment was constant. The weights required for the 

 withdrawal were for — 



grins. 



The empty watch-glass (with the cover and ring) 0'40 



The watch-glass with distilled water .... 0'28 



..« the solution 1 3*94 



II. ... 2-14 



III. . . . 1-23 



IV. ... 0-72 



If we deduct from the three weights last determined the 

 attraction of the watch-glass cover and brass ring, we get 

 the attraction of the four solutions I. to IV. But whilst in these 

 solutions the protochloride of iron is magnetically attracted, the 

 water they contain is diamagnetically repelled, and the attrac- 

 tion detei'mined above is the excess of the attraction over the 

 repulsion. 



From the two first weighings we find for the diamagnetic 

 repulsion of the water filling the entire cavity of the watch-glass, 



0*12 grm. 



Thus if in aU the solutions we neglect the volume of the proto- 

 chloride of iron in comparison with the volume of water, in doing 

 which the greatest error occurs with the strongest solutions, in 

 each case 0*28 grm. must be deducted instead of 0*40 grm. But 

 we proceed more accurately when, instead of the protochloride 

 of iron, we regard the solution I. as the original magnetic sub- 

 stance, to which in the following solutions water is added in 

 given proportions. The volumes of the water added amount to 

 \, I, and ^ of the whole volume, and hence the corresponding 

 diamagnetic repulsions, when the water is uniformly diffused 

 through the entire space, are as follow : — 



006 grm. 0*09 grm. 0-105 grm. 



• About the same proportion was used in ail the experiments described in 

 memoir. 



VOL. V. PART XXI. 3 C 



