166 



THE GARDENER'S ASSISTANT. 



Gypsum, or sulphate of lime, is a combination 

 of one equivalent of sulphuric acid with one 

 equivalent of lime. In its natural state it always 

 contains a considerable proportion of water, 

 which may be expelled by exposing it to a tem- 

 perature of 270°; it then becomes plaster of Paris. 

 One hundred parts of gypsum consist of 32*5 

 parts of lime, 46 -5 of sulphuric acid, and 21 of 

 water. Gypsum is sparingly soluble in water, 

 requiring for solution 500 times its weight of 

 cold, or 450 of boiling water. 



Many different opinions are entertained re- 

 specting the action of gypsum as a manure. 

 Some chemists consider that it acts by supplying 

 direct nourishment to plants, affording them 

 sulphate of lime, which is found in their ashes. 



Gypsum has been applied with considerable 

 success to grass, and more especially to Lucerne, 

 Sainfoin, and Clover. Good results are also 

 stated to have followed its application in the 

 case of Turnips and Potatoes. It is used as a 

 top-dressing, and at the rate of 2 or 3 cwts. 

 per acre, sometimes less, sometimes more. It 

 is found to produce the best effects when sown 

 in wet weather; and in America they are very 

 particular to use it after a shower of rain. 



The soils to which it is considered best adapted 

 are light or sandy ones, though it has also been 

 successfully used on heavy soils. The reason 

 why gypsum produces no benefit in many soils 

 is doubtless owing to the fact that lime already 

 exists in them in sufficient quantity, or that 

 they contain too little organic matter for the 

 gypsum to act upon. 



PJwsphate of Lime. — Inexhaustible beds of 

 phosphorite occur in Spain and Portugal. It 

 likewise exists in large quantities in coprolites, 

 and in bones, the fertilizing effects of which are 

 principally due to the presence of this substance. 

 All organic manures, and some kinds of chalk 

 and marl, also contain phosphate of lime. The 

 better kinds of phosphatic guanos contain a great 

 deal of phosphate of lime of a high degree of 

 purity, and easily dissolved and appropriated by 

 plant-roots. 



Phosphate of lime is found in nearly all plants, 

 and, on account of its supplying phosphoric acid, 

 constitutes a valuable addition to all soils. 



Coprolites, or the fossil excrements of animals, 

 are found in most geological strata, but more 

 especially in the greensand, lias, and Suffolk crag. 



They occur in rounded nodules, generally of 

 small size, which have a stony appearance and 

 brown colour. They consist principally of phos- 

 phate of lime, phosphate of magnesia, and car- 

 bonate of lime. Some coprolites have been found 



to contain as much as 70 per cent of phosphate 

 of lime, but in general the proportion of this 

 substance rarely exceeds 55 per cent. On account 

 of the phosphates of lime and magnesia which 

 they contain, coprolites constitute a valuable 

 manure. They are used either in a ground state, 

 or submitted to the action of sulphuric acid, 

 when they are converted into superphosphate 

 of lime and gypsum. 



Marl. — This term is employed to designate 

 various earthy substances, principally consisting 

 of clay or sand, but all containing more or less 

 calcareous matter. 



The use of marl as a manure dates from a very 

 early period. Marls may be divided into six 

 principal varieties, namely — 1. clay-marl; 2. 

 sandy marl; 3. chalk -marl; 4. slaty or stony 

 marl; 5. shell-marl; 6. peaty marl. 



1. Clay-marls are applied with great advan- 

 tage to all loose and sandy soils, the texture of 

 which they greatly improve by communicating 

 to them the requisite degree of tenacity. Peaty 

 soils are likewise benefited by the application of 

 clay-marl, the lime in which neutralizes the vege- 

 table acids in the peat. The beneficial action of 

 clay-marls is not solely attributable to the alter- 

 ation which they effect in the texture of the soil 

 they are applied to, for it is partly due to the 

 carbonate of lime they contain, and likewise to 

 their frequently affording a supply of phosphoric 

 acid, potash, and soda, often found in small 

 quantities in clay-marls. 



2. Sandy marls consist principally of sand, of 

 which they often contain as much as 70 or 80 

 per cent. The amount of lime which is present 

 in these marls is also variable. In some it occurs 

 to the extent of 30 per cent; in others it is less 

 than 10 per cent. 



Sandy marls greatly improve stiff and reten- 

 tive clays, the friability of which they much 

 increase. 



3. Chalk-marls consist principally of carbonate 

 of lime, and may be applied with advantage to 

 all soils deficient in calcareous matter, and where- 

 ever the use of chalk is attended with good effects. 

 Some chalk-marls are rich in phosphate of lime. 

 When this is the case, they are applied with ad- 

 vantage to nearly all soils, even to those which 

 already contain a considerable amount of car- 

 bonate of lime. 



4. Slaty or stony marls. Of these, some have 

 a gravelly appearance; others, that of indurated 

 clay ; some contain a considerable amount of car- 

 bonate of lime, whilst others consist principally 

 of sand, with but a small quantity of lime. These 

 marls, when exposed to the action of air, water, 



