IRON 1025 



filter and washed; the filtrate and washings are supersaturated with hydrochloric 

 acid, nearly neutralised with ammonia, and the alumina finally precipitated by car- 

 bonate of ammonia. From the weight of the ignited precipitate, the corresponding 

 amount of phosphoric acid determined by a separate operation is to be deducted, and 

 the remainder is calculated as alumina. The residue left after digesting the ore with 

 hydrochloric acid, consists principally of silica, but it may also contain alumina, per- 

 oxide of iron, lime, magnesia, and potash. For practical purposes it is rarely necessary 

 to submit it to minute examination ; should such be desired, it must be dried, ignited, 

 and weighed, then fused in a platinum crucible with four times its weight of mixed 

 alkaline carbonates, the fused mass dissolved in dilute hydrochloric acid, and evapo- 

 rated to dryness, the residue moistened with strong hydrochloric acid, and after stand- 

 ing at rest for some hours, digested with hot water, filtered, and the silica on the filter 

 ignited and weighed. The alumina, lime, oxide of iron, and magnesia in the filtrate 

 are separated from each other according to the instructions given above ; the potash is 

 estimated by a distinct process. 



Carbonic acid. This acid, which constitutes a considerable part of the weight of 

 that large and important class of ores the clay ironstones, is estimated by noting the 

 loss sustained after adding to a weighed portion of the ore sulphuric acid, and thus 

 evolving the gas; or more roughly, by the loss sustained in the entire analysis. 

 Another method is to fuse 20 or 25 grains of the ore with 60 or 80 grains of dry 

 borax, and noting the loss, which consists of water and carbonic acid ; by deducting 

 the water obtained in a previous experiment, the quantity of carbonic acid is ob- 

 tained. This method, however, can scarcely be recommended, on account of the cor- 

 rosion of the crucible, though the results are very accurate. 



Determination of the iron. This is performed on a separate portion of the ore, 

 either by the volumetric method of Marguerite, or by that of Dr. Penny: both give 

 very exact results. Marguerite's method is based on the reciprocal action of the 

 salts of protoxide of iron and permanganate of potash, whereby a quantity of the 

 latter is decomposed exactly proportionate to the quantity of iron. The ore 

 (about 10 or 15 grains) is dissolved in hydrochloric acid, and, the metal brought to 

 the minimum of oxidation by treating the solution with sulphite of soda (or better, 

 sulphite of ammonia} , and boiling to expel the excess of sulphurous acid ; the solution 

 of permanganate of potash is then cautiously added drop by drop, until the pink colour 

 appears, and the number of divisions of the burette required for the purpose accurately 

 noted. The solution should be considerably diluted, and there must be a sufficient 

 quantity of free acid present to keep in solution the peroxide of iron formed and also 

 the oxide of manganese. The whole of the iron must be at the minimum of oxidation, 

 and the excess of sulphurous acid must be completely expelled ; if the latter precau- 

 tion be neglected an erroneous result will be obtained, as the sulphurous acid will itself 

 take oxygen from the permanganic acid, and thus react in the same manner as iron. 



To prepare the permanganate of potash, 7 parts of chlorate of potassa, 10 parts of 

 hydrate of potassa, and 8 parts of peroxide of manganese are intimately mixed. The 

 manganese must be in the finest possible powder, and the potash having been dis- 

 solved in water, is mixed with the other substances, dried, and the whole heated to 

 very dull redness for an hour. The fused mass is digested with water, so as to obtain 

 as concentrated a solution as possible, and dilute nitric acid added till the colour 

 becomes of a beautiful violet ; it is afterwards filtered through asbestos. The solution 

 must be defended from the contact of organic matter, and kept in a glass-stoppered 

 bottle. If the solution be evaporated, it yields beautiful red acicular crystals : it is 

 better to employ the crystals in the preparation of the test-liquor, as the solution keeps 

 much better when no manganate is present. To prepare the normal or test-liquor, 

 a certain quantity, say 15 grains, of pianoforte wire are dissolved in pure hydro- 

 chloric acid; after the disengagement of hydrogen has ceased, and the solution is 

 complete, the liquor is diluted with about a pint of water, and accurately divided by 

 measurement into two equal parts, the number of burette divisions of the solution of 

 permanganate required to produce in each the pink colour is accurately noted ; and 

 this number is then employed to reduce into weight the result of the analysis of au 

 ore. A useful normal liquor is made by dissolving 100 grains of the crystallised per. 

 manganate in 10,000 grains of water. 



Penny's method is based on the reciprocal action of chromic acid and protoxide of 

 iron, whereby a transference of oxygen takes place, the protoxide of iron becoming 

 converted into peroxide, and the chromic acid into sesquioxide of chromium. The 

 process is conducted as follows : A convenient quantity of the specimen is reduced 

 to coarse powder, and one half at least of this is still further pulverised until it is no 

 longer gritty between the fingers. The test solution of bichromate of potash is next 

 prepared : 44;4 grains of this salt in fine powder are weighed out, and put into a 

 burette graduated into 100 equal parts, and warm distilled water is afterwards poured 



VOL. II. *3U 



