40 



and calculate the value of 1 c. c. thus : Number of c. c. perm angau ate 

 used : 1 c. c. : : weight of iron used : x $ x is, therefore, equal to the value 

 of 1 c. c. Multiply the result so obtained by 0.997 the weight of the 

 metallic iron contained in the wire. 



The standardizing of the permanganate should be repeated once or 

 twice, and the quantity of permanganate used in the several trials 

 should not diifer by more that one-tenth of a c. c. The average may 

 be taken as correct. (Fres., 112, 2, aa. Crookes, p. 73.) 



DETERMINATION OF THE LIME. 



The nitrate and washings from the hydrates are concentrated to 100 

 c. c., if possible, and 1. c. c. of ammonia added. If the ammonia pro- 

 duces a precipitate other than aluminium and ferric hydrates, which 

 must be filtered out and added to the main precipitate ' of the hy- 

 drates, acidify the solution with hydrochloric acid, boil for a minute, 

 and then make alkaline again with ammonia. This is done to introduce 

 a sufficient amount of ammonium chloride to prevent the precipitation 

 of the magnesium hydrate. Then add 40 c. c. of a solution of ammonium 

 oxalate, saturated, enough to precipitate all the lime as oxalate, and con- 

 vert the magnesia also into oxalate ; a very soluble compound of magne- 

 sia, and easily washed from calcium oxalate, which remains in solution. 

 (Fres., p. 831. Exp. 92, 93.) Heat the solution to incipient boiling, and 

 then allow it to stand undisturbed several hours. After the precipitate 

 has settled perfectly, decant the clear fluid through a filter, wash by de- 

 cantatibn once with about 25 c. c. hot water. Then dissolve the precip- 

 itate of calcium oxalate, mixed with a little magnesium oxalate, in the 

 beaker, with as little hot dilute hydrochloric acid as possible. Should 

 any of the precipitate have passed over on the filter, wash it back into 

 the acid solution, dilute with about 50 c. c. of hot water, make alkaline 

 with ammonia, and add 5 or 6 c. c. ammonium oxalate, stir, and allow 

 the precipitate to settle. When it has settled completely, filter through 

 the same filter into a fresh beaker, transfer the precipitate, and wash 

 it thoroughly with hot water. The water required to transfer the pre- 

 cipitate to the filter will wash it sufficiently. Dry the filter and contents 

 at a temperature not exceeding 100 C. to avoid making the filter brit- 

 tle. When the precipitate is dry brush it into a clock-glass, cleaning 

 the filter as thoroughly as possible. Burn the paper in a weighed pla- 

 tinum crucible until only a white ash is left. Then cool the crucible, 

 transfer the precipitate from the glass to the crucible, add enough con- 

 centrated sulphuric acid to cover the precipitate, place the lid on the cru- 

 cible, and apply a gentle beat to its edge until all the free sulphuric acid 

 is expelled. Then ignite strongly for a few minutes, cool in a desiccator 

 and weigh. This weight, less that of the crucible and filter ash, will 

 give that of the calcium sulphate. 



Never attempt to ignite the calcium oxalate before adding the sul- 

 phuric acid, as the ignition will convert it into calcium oxide or carbon- 



