No. V.\ OP THE SOLUBL*^ SAL.1NK MATTER IN THE SOTL. 33 



/. If the addition of bi-chloride of platinum to the sohition directly filtered 

 from the soil give a yellow precipitate, it contains either potash or aviraonia. 

 If, when collected on the filter, dried, and heated to bright redness in the air, 

 white fumes are given off by this yellow precipitate, and only a spongy mass 

 of metallic platinum remains behind, the solution contains aniiiionia only. If, 

 with the platinum, be mixed a portion of a soluWe substance having a taste 

 like that of common salt, and giving again a yellow precipitate with bi-chloride 

 of platinum, it contains j^oiaA'h — and if the spongy platinum contained in the 

 burned mass, after prolonged heating, amount to more than 57 per cent, of 

 its weight, or if it be to the soluble matter in a higher proportion than that of 

 4 to 3, the solution contains both po'ask and amvioma. 



The presence oi amvionia in the saline substance, or in the concentrated solu- 

 tion, is more readily detected by adding a few drops of a solution of caustic 

 potash, when the smell of ammonia becomes perceptible, or if in too small 

 quantity to be detected by the smell, it will, if present, restore the blue colour 

 to reddened litmus paper. This experiment is best made in a small tube. 



g. If, when the solvuion, obtained directly from the soil, is evaporated to dry- 

 ness, and the residue heated to redness in the air, a deflagration or burning like 

 match-paper be observed, nitric acid is present. Or, if the dry mass, when put 

 into a test tube with a litde muinatic acid, evolves distinct red fumes on being 

 heated, or enables the muriatic acid to dissolve gold-dust, and form a yellow 

 solution ; or, if to a colourless solution of green vitiiol (sulphate of iron), 

 introduced into the tube along with the muriatic acid, it imparts more or less of a 

 brown colour — in any of these cases the presence of nitric acid may with cer- 

 tainty be inferred. It will be only on rare occasions, however, that salts, so 

 soluble as the nitrates, will be found in sensible quantity in the small portion 

 of a soil likely to be employed in these preliminary experiments. 



Ji. If ammonia throw down nothing (see under r/) from the solution, and if 

 no precipitate appear when chloride of calcium or magnesium is afterwards 

 added, the solution contains no vhospkuric add. But if ammonia cause a pre- 

 cipitate, and after this is separated by the filter, nothing further falls on adding 

 either of the above chlorides, the phosphoric acid, if any is present, will be con- 

 tained in the precipitate which is upon the filter. Let this, after being well 

 v/ashed with distilled water, be dissolved off with a little pure nitric acid 

 diluted with water, and then neutralized as exactly as possible with ammonia. 

 If a solution of acetate (sugar) of lead now throw down a white precipitate, phos- 

 phoric acid is present. The phosphate of lead — the white precipitate which 

 falls — melts readily before the blow-pipe, and, on cooling, crystallizes into a bead 

 with beautiful crystalline facets. 



Or — if the precipitate thrown down by ammo)»ia be wholly or in part insolu- 

 ble in pure acetic acid (vinegar), that which is undissolved contains phosphoric 

 acid. If acetic acid dissolve the whole, it may be inferred that no phosphoric 

 acid is present in the soil. 



But if no precipitate be thrown down by ammonia, instead of the chloride of 

 calcium above recommended, a few drops of a dilute solution of alum may be 

 mixed vvith the solution, after adding the ammonia, and the whole well shaken. 

 If the white pi-ecipitate, which now falls, dissolve wholly in acetic acid, no phos- 

 phoric acid is present, and vice versa. 



These preliminary trials being made, notes should be kept of all the appear- 

 ances presented, as the method to be adopted for separating and determining 

 the weight of each substance will depend upon the number and nature of those 

 which are actually found to be present. 



14"^. Determination of the quanlMies of the several conslitue7its of the soluble 

 saline mailer. — The quantity of soluble saline matter extracted from a mode- 

 rate quantity of any of our soils is rarely so great as to admit of a rigorous 

 analysis, and the preceding determination of the kind of substances it contains 

 will be in most cases sufficient. Cases may occur, however, in which much 



