k 



25 



The most important phosphatic guanos are ]\Iexillones and 

 Sombrero, the latter contains from 70 to 80 per cent, of 

 phosphates of lime, iron and alumina. It comes from Sombrero 

 Island in the Gulfof INIexico, it is supposed to be a fossilised 

 guano and is often known as Sombrerite. 



In nearly all of the substances above-mentioned, the 

 phosphates are in such a very insoluble condition as to be 

 almost worthless as manure in their raw state, and it is to Liebig 

 we owe the process by which these phosphates are made soluble, 

 or in other words converted into superphosphates. Liebig 

 showed that if phosphate of lime which is composed of three 

 molecules of lime, combined with one of phosphoric acid, is 

 treated with a strong acid such as sulphuric, two molecules of 

 the lime are taken away to form gypsum, and the rest of the 

 lime and phosphoric acid are left in a very soluble state. 



When bones have been treated by this process, not only the 

 phosphate of lime made soluble is of value, but also that part 

 which remains only partially acted on by the acid still has about 

 the same value as raw bone. A good bone superphosphate 

 should contain about 20 percent, of its bone earth made soluble, 

 and about 10 per cent, of insoluble phosphate. The organic 

 matter should yield from two to three per cent, of ammonia. 



In superphosphates which are made from bone ash and 

 mineral matter alone, — and it has been stated that more than 

 half a million tons are used in England alone every year, — the 

 phosphates which have been made soluble are the only ones 

 which are taken into account in valuing them. By far the 

 greater quantity of superphosphates which are used are made 

 entirely from mineral matter, and as they vary a good deal in 

 quality I will give an easy and comparatively inexpensive method 

 of getting at their value. We are often told that it is quite un- 

 necessary for a farmer to be able to analyse a manure, that all 

 he has to do is to go to a respectable dealer and he is sure of 

 getting a good article, but as most dealers are not manufacturers 

 they must be at the mercy of the makers, A sample which was 

 offered in Canterbury- market as one of the best superphosphates, 

 price £6 OS. per ton, I found to contain only 6^ per cent, of 

 phosphates made soluble, instead of 25 or 26 per cent. It also 

 contained 25 per cent, of sand. Samples, too, which are 

 ^aranteed to contain a certain quantity of soluble phosphates, 

 are often considerably under the mark. 



The following is a list of the apparatus and solutions which 

 will be required : — 



A small pair of scales and weights, a 500 decern flask, 50 

 decem pipette, a burette with glass stop cock graduated to tenths 

 of a decem, a five decem pipette, wooden burette holder, a 

 small flask, small glass funnel, packet of filter paper, packet of 

 blue litmus paper, a glass rod with half an inch of India rubber 

 tubing on one end, a mortar and pestle, watch glass, spirit lamp, 

 methylated spirit one pint, wire gauze four inches square, retort 



