Thirty-eighth annual report [of the] Local Government Board. Supplement in continuation of the report of the Medical Officer of the Board for 1908-09, containing Reports and papers on the nature, uses and manufacture of ferro-silicon, with special reference to possible danger arising from its transport and storage / by S. Monckton Copeman, Samuel R. Bennett and H. Wilson Hake.

Date:
1909
Catalogue details

Licence: In copyright

Credit: Thirty-eighth annual report [of the] Local Government Board. Supplement in continuation of the report of the Medical Officer of the Board for 1908-09, containing Reports and papers on the nature, uses and manufacture of ferro-silicon, with special reference to possible danger arising from its transport and storage / by S. Monckton Copeman, Samuel R. Bennett and H. Wilson Hake. Source: Wellcome Collection.

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    silver sulphide, all the phosphorus was now present in the filtrate as phosphoric acid. Ammonia and ammonium chloride were next added, and the ammonium phosphate so formed pre- cipitated with magnesium sulphate in the usual way; the precipi- tate, after duly washing and drying, being finally ignited and weighed as magnesium pyrophosphate. From the relation [Mg2P207=2PH3] the number of cubic centi- metres of phosphoretted hydrogen, corresponding to the weight of the magnesium pyrophosphate precipitated, can be calculated. The results of all three experiments in this series were then compared, and were found, on the whole, to agree closely, although one or two of the silver estimations showed a rather higher result than was given by the gold and pyrophosphate methods. The following examples, taken from Table I. (Summary of Results), illustrate this agreement: — Number of Sample. Volume of Phosphoretted Hydrogen evolved from 10 grammes of powdered sample, calculated from :— (a.) Weight of Silver. (6.) Weight of Hold. (c.) Weight of Pyrophosphate. LI 2‘52 c.c. 2‘36 c.c. 2’50 c.c. LII 3-03 „ 2-93 „ 3-00 „ XXXIV 3-60 „ 3-61 „ 3-50 „ XXXV 1-26 „ 1-01 ,. 1-08 „ 11 **• ••• 1-63 „ 1-41 „ 1-50 „ LIX 4-74 „ 4-39 „ 4-42 „ Having established the general principle by making all three estimations on typical samples, it appeared unnecessary to do this in the case of all samples examined. In some instances, there- fore, only two estimations were made, e.g., silver and gold, gold and phosphorus, or silver and phosphorus; while occasionally reliance was placed on the silver estimation alone as sufficing to estimate the quantity of phosphoretted hydrogen present. (d.) Estimation of Alkalinity (Lime) of Samples after being acted upon by Water.—It has already been pointed out that by the reduction of calcium phosphate [Ca3 (P04)2] present in coal and quartz, calcium phosphide (Ca3P2) is liable to be formed during the manufacture of ferro-silicon. Calcium phosphide, in the pure state, is crystalline, and is decomposed by water with evolution of non-inflammable phos- phoretted hydrogen and simultaneous formation of calcium oxide or lime according to the chemical equation:—Ca3P2 + 3H20 = 3CaO + 2PH3 (Moissan). When the vapour of phosphorus is passed over lime at a red heat a so-called impure phosphide of calcium is formed which yields with water the volatile liquid phosphoretted hydrogen (P2 H4), which is spontaneously inflam- mable in contact with air (Thenard). The older chemists assumed the presence, in this compound, of a phosphide of cal- cium, of the formula CaP3, but this compound has not been isolated.