THE SOUTHERN PHOSPHATES

Otago Witness, Issue 2661, 15 March 1905, Page 9

THE SOUTHERN PHOSPHATES

Mr B. C. Aston, F.C.S.. Chief Chemist to the Agr : cultural Department, in hi? annual report, thus refeis to this subject : — — Rock Phosphate. — The discovery of large deposits of this important fertiliser in the southern portion of the colony has naturally stimulated farmers and others to ©end in samples of rocks which in any way resemble phosphate reck in order that they might be tested. Phosphate rock o.\«s its value xo the phosphato of lime — triCale.e phosphate. Ca3 (P04)2, — which it contain.-, and which 15 the fertilising constituent that the soils of this colony most need. To convert rock phesphate into a marketable article- it i? quarried, graded, calcined in kilns, and subsequently ground to a, fine powder. It is then ready for the market. It may, however, be converted into superphosphate, by the action of sulphuric acid, or into mixed fertiliser by the admixture of nitrogenous or potassium compounds, by either of which proces&os its value as a plant food 13 considerably enhanced. To assist those who are searching foi- this valuable mineral, a description of it is given, together with a few simple tests which may "be applied in the field. New Zealand phosphate, hitherto found in the colony in workable, quantities only at Mil burn and Clarendon iOtago), ha^s a dirtyyellowish, white, or light-grey colour. It is easily distinguished from limestone, which it resembles, in not effervescing when brought into contact with a drop of dilute hydrochloric, sulphuric, or nitric icid. it is harder and heavier than limestone, and has no trace of crystalline structure. It is with difficulty scratched by a knife blade, but it is softer than feldspar and than mest silicate rocks liable t<. be mistaken foi phesphate and which a knife-blade will not scratch. Some- phosphates have a tendency to exfoliate, or shed their fragments in layers, when struck with a hammer. Phosphate rock should b& looked for in all limestone districts. The deposit at Clarendon rests directly on limestone. A limited number of specimens of New Zealand phosphate rock are available for distribution to farmers, prospectors, and others interested, and will be sent free on application. If, therefore, a rock is found which is — 1. Dirty white, ye'lowish, or greyish white in colour ; 2. Softer than quartz and feldspai-, but harder than limestone ; 3. Heavier than limestone and quartz; 4. Non-crystalline : 5. Does not effervesce with acid,~ a small specimen in the first instance should b& sent by post to the Department's chemical laboratory for analysis. The sample will ba tested and reported on free of charge. Sample^, applications, etc., should be sent to the Chief Chemist, Department of Agriculture, Wellington. * A very good test that may be applied by those who have necessary materials is to .grind the suspected rock to a fine powder, and place about as much as will lie on a three-penny-bit, with, about half an inch of raagne3XK.ua ribbon, in a piece of glass tube which has been drawn out a.nd closed at one end in the flame. The tube is then heated to redness over a- lamp or candle, or with a mouthblowpipe, until the magnesium kindles, and then plunged into cold water. If any phosphato is present in quantity a few bubbles of gas, consisting ,of hybrides of phosphorus, ■will he format! and -will eaummiiieate t-o tbe watsr and air a putrid metallic smell wh/ch is most characteristic, and recalls the odour cf decaying fish. This smell may often be noticed near an aeetylane-generating plant.