32 OF THE SOLUBLE SALINE MATTER IN THE SOIL. [AppCndtX, 



separate portions are to be put into so many clean wine glasses, and the effect 

 produced upon these by different chemical substances carefully noted. 

 If with a few drops of— 



a. Nilrate of Baryta^ it gives a white powdery precipitate, which does not 

 disappear on the addition of nitric or muriatic acid, the solution contains sulphu- 

 ric acid. If the precipitate does appear, it contains carbonic acid. In this lat- 

 ter case, the liquid will also effervesce on the addition of either of the acids 

 above mentioned. 



b. If with oxalate of ammonia, it gives, either immediately or after a time, a 

 white cloud, it contains lime,* and the greater the milkiness, the larger the 

 quantity of lime may be presumed to be. 



c. If with nitrate of silver, it gives a white curdy precipitate, insoluble in pure 

 nitric acid, and speedily becoming purple in tlie sun, it may be presumed to 

 contain chlorine. 



(l. If with caustic ammonia, it gives a pure white gelatinous precipitate, it 

 contains either alumina, or magnesia, or both. In this case, muriatic acid must 

 be added till the precipitate disappears, and the solution is distinctly acid. If 

 on the addition of ammonia in excess, the precipitate reappears undiminished 

 in quantity, it contains alumina only. If it be distinctly kss in quantity, we 

 may infer the presence of both magnesia and alumina ; and if no precipitate now 

 appears, that it contains magnesia only. If a large quantity of magnesia be present, 

 it may be necessary to re-dissolve and acidify the solution a second time be- 

 %re, on the 7-^-addition of ammonia, the precipitate would entirely disappear. 



If the precipitate, by ammonia, have more cr less of a brown colour, the pre- 

 sence of iron, and perhaps manganes?, may be inferred. If, on the second 

 addition of ammonia, the colour of the precipitate has disappeared, it has been 

 due to the manganese only— if it still continue brown, it is owing chiefly or 

 altogether to the presence of oxide of iron. If the colour of the precipitate, by 

 ammdnia, be very dark, it consists almost entirely of oxide of iron, and may 

 contain little or no alumina, — when it is only more or less brown, the presence 

 of both alumina and oxide of iron may with certainty be infeired. 



e. If, after the first addition of ammonia, the solution be filtered to separate 

 the alumina, the oxides of iron and manganess, and the magnesia that may be 

 thrown down — if oxalate of ammonia be then added till all the lime falls, and 

 the liquid be again filtered, evaporated to dryness, and then heated to incipient 

 redjiess in the air, till the excess of oxalate of ammonia is destroyed and driven 

 off — and if a soluble residue then remain, t it is probable that potash or soo'a, or 

 both, are present. If, on dissolving tliis residue in a little water, the addition of 

 a few drops of a solution of tartaric acid to it produce a deposite of small 

 colourless crystals (of cream of tartar), or if a drop of a solution of bi-chlo- 

 ride of platinum produce in a short time a yellow powdery precipitate, it con- 

 tains potash. If no precipitate is produced by either of tliese — re-agents as they 

 are called — the presence of soda may be inferred. If the yellow precipitate, 

 containing potash and platinum, be separated by the filter, and the solution, after 

 being treated with sulphuretted hydrogen and filtered to separate the excess of 

 bi-chloride of platinum, be evaporated to dryness — if, then, a soluble saline 

 residue still remain, the solution contains soda as well as potash. 



It is to be observed that some magnesia, if present, may accompany the pot- 

 ash and soda through these several processes. After the separation of the potash, 

 a little caustic ammonia will detect the presence of magnesia, but it will rarely 

 be found so far to interfere with ih\s preliminary examination as to prevent the 

 experimenter from arriving at correct results (see p. 35, /). 



* Tlie learned reader will understand why, for the sake of simplicity, I take no notice of 

 substances not likely to be present in the soil— as, for example, baryta, which would here be 

 thrown down along with the lime, or of oxalic acid, which, equally with the sulphuric or car- 

 bonic (a), woulcyjive a white precipitate with nitrate of baryta. 



t Not precipiwed from its solution by ammonia, for if precipitated it 13 partly at least 

 chloride of magnesium. 



