in the Isle of Wight. 233 



To ascertain the quantity of this substance, a variety of methods 

 was used, the principal results of which I shall cursorily relate, 



2. It would have been in vain, in this instance, to have applied, 

 without any previous step, oxalat of ammonia, the usual test of lime» 

 in order to obtain an accurate estimate of the quantity of lime pre- 

 sent in the water ; for as oxalic acid also acts upon iron, some ambi- 

 guity would necessarily have occurred. Indeed that oxalat of ammo- 

 nia did not, in this case, re-act upon the lime in the manner that it 

 usually does, had been noticed (§ III. f, g) in some of the prelimi- 

 nary experiments*. 



* By adding a considerable quantity of oxalat of ammonia, and concentrating the 

 solutions by heat, (he whole of the lime appeared to be precipitated, together with a 

 portion of iron ; but in order to obtain the oxalat of lime pure, it was necessary to cal- 

 cine the precipitate so as to drive off the oxalic acid, to redissolve the residue in muriatic 

 acid, and to precipitate the lime again by oxalat of ammonia. The small quantity of iron 

 present did not ^Aen interfere, and this process, however circuitous, proved tolerably 

 accurate. 



I was drawn by this part of the subject into an experimental inquiry respecting the 

 action of oxalat of ammonia on solutions of iron, and the unfitness of that test for the 

 precipitation of lime when iron is present, the principal results of which I shall state 

 summarily. 



1. If to a strong solution of sulphat of iron, a small quantity of sulphat of lime be 

 added, and then a little oxalat of ammonia, no precipitate or cloudiness appears ; whilst 

 the same quantities of sulphat of lime and oxalat of ammonia added to a bulk of water 

 equal to that of the solution of iron, instantly form a precipitate. 



2. If oxalat of ammonia be added to a solution of sulphat of iron, a bright ycllovir 

 colour is produced, and presently after this a copious white precipitate appears, which, 

 in subsiding, assumes a pale lemon colour. If at the moment the cloud is forming, the 

 vessel be scratched with any pointed instrument, white lines appear, as in the precipita- 

 tion of magnesia from carbonic acid by phosphoric acid. 



3. This precipitate being washed, and gently heated over a lamp, assumes a bright 

 cinnamon colour, and becomes magnetic, in consequence, no doubt, of the carbonization 

 of the oxalic acid, and these changes take place at a heat much inferior io ignition. 



2g 



