Ohservatiotis on Liehigs " Organic Chemistrjj." 131 



phuiic acid (vitriol), diluted with three or four parts of water; 

 after digesting for some time, add 100 parts of water, and 

 sprinkle the mixture over the field before the plough. The sul- 

 phuric acid will dissolve, but not decompose, the phosphates, 

 unless partially; and the free acid unites with the alkalies in the 

 earth, and a neutral salt (probably gypsum) is formed, in a 

 very fine state of division. In the manufiictories of glue, he 

 says, many hundred tons of a solution of phosphates in muriatic 

 acid are yearly thrown away as useless; this solution, he thinks, 

 miffht be substituted for bones. The free acid would form mu- 

 riate of lime (chloride of calcium), which has a great affinity 

 for water, and might supply the place of gypsum, in forming 

 inuriate of ammonia and carbonate of lime. The ashes of brown 

 coal and peat contain also potash and phosphates. It is of much 

 importance, he says, that the mode of action of all these sub- 

 stances should be known ; and he illustrates this by the way in 

 which iodine is now used in medicine, instead of burnt sponge, 

 and phosphate of soda in place of cow-dung in calico-printing ; and 

 says we may one day manure our fields with a solution of glass 

 (silicate of potash). In this country soda is generally used as 

 the flux for glass. We may also purchase phosphates of mag- 

 nesia, he says, as we now do medicines from the apothecary. 

 Some plants, he continues, require humus ; others can do without 

 humus, and give it off as excrement. 



Having now considered what was necessary for supplying 

 plants with the other requisites; he proceeds to consider the pro- 

 duction of nitrogen, vv-hich abounds in all parts of plants, but 

 especially in the seeds and roots. The atmosphere furnishes it, 

 he says, in quantity sufficient for the existence of plants, to pre- 

 vent their extinction ; but the complete developement of the 

 cultivated plants in sugar, starch, and gluten cannot be obtained, 

 unless we affiird nitrogen sufficient. The nitrogen in the ffeces 

 of animals which feed on plants is not so great in quantity as 

 in those which feed on flesh ; and the faeces of human beings 

 diffi^r in this respect according to their feeding. The faeces of 

 cattle are of most use in soils which contain little potash ; the 

 fgeces of men are most useful in clay soils. It is the urine in 

 the manure which contains the ammonia. He takes the analysis 

 of urine by Berzelius, which contains mostly salts of ammonia, 

 water, and urea; the urea in this analysis is 3 per cent; the muriate 

 and phosphate of ammonia about 0*3 per cent ; and the free 

 lactic acid, lactate of ammonia, and animal matter, I'V; mucus 

 0"032, and other salts about 1"52 per cent. The urea in human 

 urine, according to Henry, is partly lactate of urea, and partly 

 urea in a free state. When it putrefies, the lactate of urea is 

 converted into lactate of ammonia, and the urea which was free 

 into carbonate of ammonia : this last is retained in solution till 



K 2 



