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advance them at all g . It should therefore be considered, whether anysalts do universally nourish all plants alike ; or rather partly, some oneplant, some another: for upon the clear decision of this secret, dependsall that is truly curious in this affair ; laying, as I do, for position, thatthe improvement of all the Earths and soils I have spoken of, resultsfrom some salt or spirit, (call it which you please,) as from an indispens-able principle in this vegetation, and perhaps the first rudiment of life inall things else > and till we shall arrive to this, (by what I have observedin the discreet use even of our common salt, brine, the effects of urineand the like) I firmly believe, that were saltpetre (I mean factitious nitre)to be obtained in plenty, we should need but few other composts to me-liorate our ground'; since whether that which so fertilizes it, by any mix-ture we can yet devise, effect it from any other cause, is greatly to bedoubted 5 nor do I think but the charge of extracting it (at least sufficientto impregnate water in convenient quantity) might be compafsed by theindustrious farmer without much inconvenience or difficulty, were hecompetently instructed in the procefs of calcination, resolution, percola-tion, evaporation, and separation, put into honest English , and easily tobe learned: soon we should then see that this were not to be extractedaltogether out of stinking dung, and found in heady trash,. (which yet ismaterial,) but rather in the well-impregnated and natural Mould itselfcharged with a more generous spirit, or medicinal nitre, (in congrefs witha certain sulphur,) capable of warming and exciting to vegetation, beyondall we can promise from any mere artificial ferments, much lefs our com-mon mixtures and ways of stercoration, which in time grow cold andlanguish, and are so quickly checked b .
, Without multiplying distinctions, we may divide manures into four kinds:
1. Such as give nourishment only, as rape-dust, soot, malt-dust, -blood compost, horn,shavings, pigeons dung, and all top-drefsxngs.
2. Such as give nourishment, and add to the soil; as horse dung, cows dung, humanordure, rotten animal and vegetable substances.
3 Such as open the soil, and do not nourish in their own-natures; as-lime, light marls,
sand, and vegetable ashes. .
4, Such as stiffen the soil, and at the same time nourish a little ; as clay, clay marls, andearth.
fc AH the boasted compositions of nitre, and other salts, for increasing the fertility of landwithout other afsistance, are now experimentally found to be of little value. ■ Hung, that is-putrid animal and vegetable substances, constitutes the only fertilizer for the use of the-