No. V.\ or THfc- SOLUBLE SALINE MATTER IN THE SOIL. 39 



ed, till on treating with water and ammonia, as before, no more alumina ap- 

 pears. 



b. Or that portion of the soil on which hot muriatic acid refuses to act may 

 be mixed with twice its weight of carbonate of soda, and heated in a platinum 

 crucible till the whole is completely fused. The mass is then to be treated with 

 diluted muriatic acid till every thing soluble is taken up, the filtered solution 

 evaporated to dryness, the dry mass moistened with muriatic acid, and again 

 treated with water. If any thing is left undissolved it will be silica, and if any 

 alumina be contained in the solution, it will be precipitated by ammonia, and 

 may be collected, washed, dried, and weighed, as already described. The so- 

 lution may also be tested for magnesia, and if any be present it may be sepa- 

 rated by the process already explained. 



The former of these two methods is to be preferred as the simpler, though it 

 will also require considerable care and attention. That which the sulphuric acid 

 leaves behind must be washed, dried, heated to redness, and weighed. It will be 

 found to consist chiefly of quartz sand, and finely divided siliceous matter. 



The accuracy and care with which the whole of these processes have been 

 conducted is tested by adding together the weights of the several substances 

 that have been separately obtained. If this sum does not differ more than one 

 per cent, from the weight of the soil employed, the results may be considered 

 as deserving of confidence. One of the points in which a beginner is most 

 likely to err, is in the washing of the several precipitates he collects upon his 

 filters. As this is a tedious operation, he is very likely to wash them, at first, 

 only imperfectly, and thus to have an excess of weight when his quantities are 

 added together — whereas a small loss is almost unavoidable. The precipitates 

 should always be washed with distilled water, and the washing continued until 

 a drop of what passes through leaves no stain when dried upon a bit of glass. 



No. VI. 



ACTION OF GYPSUM. — {See pages 333-34.) 



In the text I have stated what appear to me the most probable effects which 

 gypsum is fitted to produce upon the soil. Some of the numerous opinions that 

 have been entertained upon this point are thus summed up by Hlubeck : — 



" According to i^oZ^?^e?•, the action of gypsum depends upon the power pos- 

 sessed by lime to form with the oxygen and carbon of the atmosphere compounds 

 which are favourable to vegetation ; accoiniing to Ritckert, it acts like any other 

 food ; according to May.r and Brown, it merely improves the physical proper- 

 ties of the soil ; while, according to R:U, it is an essential constituent of the plant. 

 Hedwi g caWedi gy^sxxm the saliva and gastric juice of plants ; Huviholdt , Gir- 

 tanir, and Albc.rl ^Pkaer considered it as a stimulant by which the circulation 

 of plants is promoted ; and CfiapUil ascribed its action to a supposed power of 

 supplying water and carbonic acid to plants. Davy regarded it as an essential 

 constituent of plants, because it acts only where gypsum is wanting in the soil, 

 while other English agriculturists have supposed it to promote fermentation in 

 the soil. According to Laxihender , it acts as an exciting power without mixing 

 itself with the sap of the plant; according to Lieblg, it fixes the ammonia of the 

 atmosphere ; and, according to Brcfonnot and Sprcngel, it supplies sulphur 

 for the formation of the legumin of the leguminous plants (the most probable 

 view)." — Erndhrung der PJlanzcn, p. 70, note. 



To the above extract I may add, tiiat Mr. Cuthbert Johnson ^o long known 

 for his many valuable writings upon agriculture, in following out the above idea 

 of Reil and Davy in a recent paper on the use of gypsum (Jour, of the Royal 

 28° 



