The following is another good method of determining the sulphur in a sample of coal :—Make mixture of 1 part of the finely powdered coal, 8 parts of nitre, 16 parts of common salt, and 4 parts of carbonate of potash, all of which should be pure. Place the mixture iu a platinum crucible, and heat it gently ; after a time the contents will take fire and burn. Then raise the heat until the mass fuses, and maintain the temperature until it becomes quite white. Allow it to cool, and dissolve it in water. Filter, add hydrochloric acid and chloride of barium, and proceed as in the above case.
Assay of Guano.—(1) Moisture.—Weigh out 5 grm. in a platinum or porcelain crucible, and dry in a water-bath until the weight is constant.
(2) Total Fixed Constituents.—The dried residue from the above operation is to be ignited at a low red heat till all organic matter is consumed, when the residue will be greyish white in colour ; the weight gives the percentage of fixed constituents, and acts as a check upon the subsequent results.
(3) Insoluble Matter.—The residue from the above operation is to be boiled with dilute hydrochloric acid until all the soluble matter is dissolved ; the residue is then to be filtered, washed, dried, ignited, and weighed ; the weight gives the amount of insoluble matter in the sample.
(4) Phosphoric Acid.—Dilute the filtrate from the above operation to 500 c.c. Take 250 c.c. and add ammonia in excess, to precipitate phosphate of lime and magnesia ; redissolve in acetic acid and divide the solution in half. One portion is to be tested for phosphoric acid by what is termed the "uranium method." Three solutions are required for this process :— 1. Standard uranium solution, prepared by dissolving about 35 grm. of crystallized uranium acetate or nitrate in 900 c.c. of water, and adding 25 cc. of glacial acetic acid. 2. Sodium acetate solution, made by dissolving 100 grm. in 900 c.c. of water, and making up to 1 litre with strong acetic acid. 3. Standard calcium phosphate, made by dissolving 4.336 grm. of that salt iu a small quantity of nitric acid, and making up to 1 litre with water. The solution must be standardized by determining the amount of phosphoric acid present with molybdic acid, as described in the hand books of analysis. The uranium solution is now diluted with water until 20 c.c. are exactly precipitated by 50 c.c. of the phosphate solution. Fifty c.o. of the latter are placed in a beaker ;
5 c.c. of acetate solution are then run in, and afterwards about 10 c.c. of the uranium solution, with constant stirring. After this it is added more slowly, in quantities of about 1 c.c., or 0.5 c.c. at a time, testing the liquid as follows, after each addition. A few drops of the liquid in the beaker are brought upon a porcelain slab, and brought into contact with a small crystal of ferrocyanide of potassium; a reddish-brown coloration ehows that xcess of the uranium bolution has been added. If there is no coloration, the addition of test-solntion is confirmed until a drop of the liquid, when tested with fermcyauide of potassium, shows that a slight excess has been run in. The requisite quantity of water is now added to the solution in order that 21 c.c. shall exactly correspond to 50 c.c. of the phosphate solution. Every cubic centimetre of the uranium solution of this strength corresponds to 0.05 grm. of phosphoric acid.
Having made these aolutions, and brought the uranium solution to the correct strength, it is easy to apply the process to the estimation of the phosphoric acid in the sample of guano, 50 c.c. of the acetic acid solution being treated exactly as described above. The uranium solution should be checked with the standard phosphate solution every time before using, and two or more estimations of the same sample ehould be made. About the same quantity of sodium acetate must bo used in each teat.
The other half of the acetic acid solution may, if it be required, be tested for lime, mag nesia, and allmlies.
(5) Ammonia.—One grain of the guano is carefully weighed out and placed with a little water in the small flask A, Fig. 283 ; the tube d is filled with a strong solution of caustic mag nesia ; the larger flask B contains an accurately measured quantity of standard sulphuric acid which has been poured through broken glass contained in the tube c. The apparatus being made quit,e air-tight, a portion of the magnesia is caused to flow into the flask A by opening the clip; it ie then heated by a Bunsen lamp until the c,ontents are brought to gentle ebullition.
Great care must here be taken, by regulating the heat, to prevent any tendency to boiling over or frothing, to which the contents of the I.