THE CHEMISTRY OF THE SOIL. L09 



residue thus left. A perfectly pure sample should volatilise completely, Leaving 

 the spoon perfectly clean. If a little of the powder be mixed with slaked 

 lime, and heated in the Bpoon, a strong smell of ammonia will be given off. 

 If there is none, the substance is not sulphate of ammonia at all, nor any 

 ammonium compound. 



I dissolve a little of the salt in water, and add a few drops of ferric chloride, 

 which can be prepared by dissolving a little iron rust, scraped off a rusty 

 iron implement, in hydrochloric acid. If a deep blood-red colour is produced 

 by this reagent, the manure should not be used, as it contains a compound 

 which is injurious to plants, namely, ammonium sulphocyanide. The solution 

 of sulphate of ammonia should not alter the colour of blue litmus paper ; if 

 it turns red, the salt contains free acid and should not be used. 



Kainit should be a crystalline powder, resembling common salt, more or 

 less white, often of a reddish or darkish tinge, generally damp to the touch. 

 It should dissolve almost entirely in water, and should be completely soluble 

 in water to which a little hydrochloric acid has been added. The potash 

 cannot be estimated by any simple method -with any degree of accuracy. 



The above tests require no other reagent than a little hydrochloric acid 

 and ammonia, and though they are not, in any sense of the word, accurate 

 analyses, still they may prove useful when there is any doubt about the 

 purity of any of the substances in question. 



With the help of a balance which will indicate half a grain, such as any 

 druggist possesses, the following scheme will. enable a fairly close estimation 

 of bonedust to be made : — 



The following articles and chemicals will be required : — A balance (turning 

 to ^ grain), pure hydrochloric acid, pure ammonia, a packet of cut filter 

 papers, glass beaker, pestle and mortar, a sieve of eighty meshes to the linear 

 inch, a porcelain basin, a glass funnel, some strips of litmus paper. These can 

 all be obtained at the local druggists. 



It is very important to obtain an average sample of the bonedust. To do 

 this, if the sample is contained in one bag, empty it out upon a clean board 

 or fioor, and mix it w-ell with the shovel. If in two or more bags, take a 

 sample from the middle of each bag, and mix them as above. From the 

 mixture take about a spadeful and grind it thoroughly in the mortar until 

 the whole of it has passed through the sieve. The sifted sample is again 

 mixed and is ready for analysis. 



A piece of glazed writing-paper is placed on one of the pans of the balance, 

 and exactly counterpoised by placing a similar piece of paper in the other 

 pan. Weigh out exactly 200 grains of the finely-powdered manure upon the 

 paper, introduce it without loss into the iron spoon, heat very gently at first 

 and then gradually more strongly until the ash is white. Care must be taken 

 not to lose any by spurting. Allow to cool; empty back again upon the paper 

 without loss of substance. The weight should not now much exceed 80 grains. 

 This is now emptied again into the porcelain basin, about half a pint of 

 water added, and about 3 ounces of strong hydrochloric acid. Boil well for 

 about five minutes, add a little more water, and filter. 



Filtering is done as follows : — Fold one of the round papers in half i ^-~n , 

 now fold again in half at right-angles to the first fold fl. On opening this 

 out it will be found to fit exactly into the funnel. The funnel with the filter 

 paper is now supported over a beaker. The liquid in the dish is poured 



