ANALYSIS. 



laceous particles, or the clay and all j 

 the matters held in suspension in the j 

 water, are thrown upon a filter and \ 

 dried ; the desiccation is completed 

 by the same process, and under the 

 •ame circumstances as that of the 

 «oil had been. The sand is, in like 

 nanner, dried with the same care. 



If we would ascertain the nature 

 and quantity of the soluble salts, the 

 whole of the water used in the wash- 

 ing must be put together and evapo- 

 rated, which may be done upon a 

 sand bath. The evaporation is push- 

 ed to dryness, and the salts that re- 

 main, having been previously weigh- ^ 

 ed, are thrown into a small platinum 

 capsLde, in which they are heated to 

 a dull red by means of a spirit-lamp, 

 in order to burn out the organic salts, 

 and thus distinguish, by means of a 

 subsequent weighing, between them 

 and the inorganic salts. 



The sand may be silicious or cal- 

 careous. The presence of carbonate 

 of lime is readily ascertained by treat- 

 ing it with an acid wiiich will form 

 a soluble salt with lime, such as hy- 

 drochloric, nitric, or acetic acid. Ef- 

 fervescence shows the presence of 

 a carbonate, the quantity of which 

 may be estimated by weighing the 

 sand dry before and after its treat- 

 ment with the acid, particular care 

 being, of course, taken to wash the 

 remaining sand well before setting it 

 to dry. Tiiis, however, is an opera- 

 tion of little use ; the great object is 

 to ascertain the quantity of sandy 

 matter. Had we a particular inter- 

 est in ascertaining the presence and 

 estimating the quantity of the earthy 

 carbonates contained in a sample of 

 soil, it would be advisable to make a 

 special inquiry, inasmuch as the fine- 

 ly-divided calcareous earth being car- 

 ried ofT along with the clay in the 

 course of the washing, the sand ob- 

 tained never contains the whole of 

 the carbonate of lime. 



The argillaceous matter procured 

 by the washing is far from being pure 

 clay ; it contains a quantity of ex- 

 tremely fine sand, particles of calca- 

 reous earth, and if the soil contain 

 humus, the more delicate particles 

 16 



of this substance "will also be inclu- 

 ded. 



To determine the quantity of hu- 

 mus, recourse is generally had to its 

 destruction by heat. A known weight 

 of dried earth is lieated to redness in 

 a capsule, and constantly stirred for 

 a time, and when no more of those 

 brilliant points or sparks, which are 

 indications of the combustion of car- 

 bon, are observed, it is set to cool, 

 and then weighed. This is the meth- 

 od which has been generally followed 

 by Davy and others. It would be 

 difficult to find a method more con- 

 venient than this, but it is, unfortu- 

 nately, very inaccurate. Soils dried 

 at a temperature at which organic 

 matter, such as humus, &c., begins 

 to change, still retain a considerable 

 quantity of water m union with the 

 clay. This water is disengaged at 

 the red heat required for the combus- 

 tion of the organic matters ; and as 

 their quantity is estimated by the loss 

 of weight on the subsequent weigh- 

 ing, it is obvious that the loss from 

 the dissipation of water is added to 

 that which proceeds from the de- 

 struction of the humus. It is un- 

 doubtedly to this cause of error that 

 we must ascribe the large proportions 

 of humus mentioned in the soils ex- 

 amined by Thaer and Einhoff; it is 

 therefore better to restrict the exam- 

 ination to the determination of the 

 presence or absence of humus than 

 to attempt to ascertain its quantity 

 by so imperfect a method. 



Priestley and Arthur Young were 

 already aware that a more delicate 

 operation was required to determine 

 the quantity of humus. They recom- 

 mend calcination of the soil in a close 

 vessel, and that the gaseous products 

 should be collected. This mode of 

 proceeding, however, would have but 

 slight advantages over that which I 

 have just criticised, inasmuch as the 

 volume of gas collected varies with 

 every difference of heat employed. 



The only method, in my opinion, 

 which we have of learning the quan- 

 tity of humus, of organic debris, 

 which is contained in a sod, is that 

 of an elementary analysis. It is by 



