iil;.she.! by John B. Rvssi;ll at thejcorner of Congress and Lindall Streets, (entrance from Kindall Street) Thomas G. Pessenbkn, Editor. 



OL. V 



BOSTON, FRIDAY, DECEMBER 8, 1826. 



No. 20. 



AGRICULTURE. 



llx 



,1 



i< theo'y of the operation o/g^ypsum or plaster 

 Paris, in promoting- the groicth of plants. 



BY JOHN GOhllAM, M. D. 



Ill the period of tlie introduction of sulphate 

 0. iiypsuni, or plaster of Paris, into agricul- 

 niddo iu which it operates in fertilizing 

 or perhaps more correctly in facilitating the 

 'J; of vegetables, has been a subject of much 



tion. The question is not yet decided, nor 



biy can it be determined, until, by long con- 



oliservation, and repeated experiment, a 



\tcnsive series of facts aiiall have been col- 

 li and properly arranged. From what is al- 



known, however, on this subject, various 

 jsions have been drawn and at present we 

 content ourselves w'ith that theory which 

 ccords witli the acknowledged properties of 

 ni, with the nature and qualities of soils and 

 the economy of the vegetable system. I pro- 

 briefly to e.xamine the plausibility of the dif- 

 t modes of e.\planation which have been of- 



on the action of this compound, and after- 

 i to state the theory which appears to me 

 obviously to flow from a view of the few facts 

 xperience and observation have established. 

 ; opinion respecting the operation of plaster 

 ris, the most generally adopted is tliat, which 

 ses it to depend on its power of absorbinr or 

 ing moisture. It has been said that dew is 



more plentifully on those parts of a field, 

 vhich the plaster in powder has been diffus ; 

 an on those which received no gypsum, if 

 je the case, it must be owing either to the 

 m being a better conductor of heat than the 

 with which it lies in contact, or to its power 

 racting water from the atmosphere. Were 

 aster in large masses, its heat might be con- 

 d off more rapidly than th;it of the surface of 

 round ; its temperature would thus be dimin- 



or it would become comparatively cool, and 

 ie rendered capable of condensing the aquc- 

 apour contained in the air continHally pass- 

 ver its surface. But the plaster is applied in 

 irni of pow der ; in that state its conducting 

 r must be diminished, and it is very probable 

 t can neither acquire nor lose its heat with 

 er rapidity than the soil with which it is mix- 

 The truth of the assertion above mentioned is 

 questioiable ; it is supported on doultful au. 

 y, and it is not advanced with that confidence 

 1 accompanies the expression of a fact which 

 liversiilly acknowledged. The idea of its 

 attraction for moisture, appears to have 

 n from the fact that gypsum products the 

 obvious and the most beneficial effects on dry 



from which it may be supposed that plants 

 Dt always derive the quantity of water neces- 

 to their crowth and vigour. But even on the 

 Jsition that it does possess, even in a very 

 derable degree, the property of imbibing 

 lire, it can hardly be supposed that the ex- 



of this power is such, as to supply a rich 

 th of vegetables with additional water, which 



be sufficient to pro luce a vegetation more 

 ■iant than in ordinary circumstances. The 



."•uouiit of the powder of gypsum distribulcil over 

 an acre i.s from two to three bushels, the layer 

 consequently is very thin ; it soon becomes mixed 

 with the rest of the soil ; it tlien e.\ists only in 

 siiiiill proportions, and it is ditfionlt to conceive 

 that in this state, it can absorb much moisture 

 from the air. Besides in some cases, for example, 

 where it is intended to accelerate the growth of 

 Indian corn, it is often applied immediately to the 

 .seed, in the proportion of about a tea spoonful to 

 each hill, and like the seed i.s covered witli a lay- 

 er of earth. In this situation it cannot be suppos- 

 ed to attract moisture from the air, nor is it more 

 evident how it can exert any influence in this res- 

 pect on the neighboring soil, for it is impossible 

 to conceive that even thcs'- substances which ii-e 

 known to possess the most powerful attraction for 

 water, could, in this proportion, afford any consid- 

 erable part of this fluid which is taken up in such 

 large (juantities by every healthy plant. The 

 sphere of this attraction must in these circumstan- 

 ces be very limited, and if the soil immediately in 

 contact with the gypsum, were to yield its fluid 

 to this compound, we have no reason to suppose 

 that it would be immediately supplied from that 

 more remote, and thus establish a current, if the 

 expression be not too strong, toward the seeds and 

 roots of the plant. As the corn which has been 

 treated in this way generally (if not always) flour- 

 isies more vigorously than when left to the pow- 

 ers of the soil alone, we may infer that the gyp- 

 si m continues to act, after it has acquired a con- 

 siJcrable height. It therefore appears absurd to 

 say that a spoonful of this compound should thus 

 be able to furnish, or should thus become the 

 means of supplying any considerable portion of 

 the water necessary to the sustenance of a large 

 plant for weeks, even granting its strong attrac- 

 tion for tliat fluid. I may now, however, observe 

 that from our knowledge of the composition and 

 properties of gypsum, we may saiely deny that in 

 its ordinary state it possesses this property in any 

 degree, more than other earthy bodies, whose 

 particles are not strongly coherent. It never ex- 

 hibits this property, unless it has been exposed to 

 heat. Gypsum is a compound of lime, sulphuric 

 acid, and water. When exposed to a high tempe- 

 rature in a solid state, it loses the water necessa- 

 ry to its constitution, and falls into powder. The 

 remaining compound of lime and sulphuric acid 

 has then a powerful attraction for this fluid, and 

 when they are mixed with each other, care having 

 been talten that the quantity of water added should 

 not exceed that which has been evolved, the semi- 

 fluid again becomes a solid : a fact which is sufli- 

 ciently familiar in the formation of stucco. When 

 thus formed anew, the attraction for water ceases, 

 for the gypsum remains dry and solid, while those 

 salts or compounds which possess this property in 

 the greatest degree, aie the most deliquescent or 

 the most disposed to become liquid on exposure to 

 the air, or moisture. Whence it appears that the 

 natural compound of lime and sulphuric acid, at 

 leist that which is most common, and the only one 

 employed in agricultirre, is already saturated with 

 water, that it is not deliquescent, and therefore 

 that there is no probability, in reasoning from ob- 

 servation independent from direct experiment, that 



it has' the smalkst additional attraction for that 

 fluid. It may p^rliaps be thought that'the effects 

 of gypsum on plunts might bo augmented by the 

 use of the powder after its water had bec.i dissi- 

 pated by expo.suie to heat. But a moment's rc- 

 tlectiou will be sufficient to convince us that no 

 additional advant.vge could be gained by this ex- 

 periment. When ileprived of its water, the at- 

 traction of the remainder for this fluid is so pow- 

 erful that it would readily absorb as much as was 

 r<}quir,ed from the soil, but this water, instead of 

 befng trnnsniilted to the roots of vegetables, would 

 be arrested and combined with the other ingredi- 

 ents, and ordinary gypsum must of course be the 

 result. 



From what has been observed it may be justly 

 suspected, if not actudly believed, that the agen- 

 cy of gypsum in promoting the growth of plants, 

 cannot with propiiety, be ascribed to its power of 

 absorbing or attncting moisture. 



i. It has been thought by many that gypsum 

 operates by aeceleratin,g putrefaction, or by pro- 

 moting the decomposition of animal and vegetable 

 matter. 



It is much to be regretted that on purely practi- 

 cal subjects, and perhaps on none more than that 

 of agriculture, we should content ourselves with 

 loose and hypothetical opinions, unsupported by 

 facts or experierce. It would not bo a difficult 

 task for any gentleman farmer, with even a super- 

 ficial knowledge of chemistry, to reduce a multi- 

 tude of supposed truths to the test of experiment, 

 and the result s\oald probably be equally useful 

 and honorable. If gypsum operate in tUo ~..j i 

 nave just mentioned, it mosfMse cither, 1 . by loos- 

 ening the soil and thus allcTinga freer access to 

 the air, light, heat and moisture, or, 2. by increas- 

 ing the temperature of the materials, or, 3. by af- 

 fording sometlung cajable of exciting and contin- 

 uing the fermentative process. 



Some advantages niiiy possibly be derived from 

 gypsum by its mechanical effects of opening the 

 soil or rendering it less dense ; but when we con- 

 sider that it is added ia comparatively small pro- 

 portions and that in some cases it produces its spe- 

 cific actions, though afplied immediately to the 

 seeds or roots of the vegetable in even minute 

 quantities, this effect at best can be regarded only 

 as trivial. If the soil be composed principally of 

 animal and vegetable matter, there is no doubt but 

 that much greater benefit may result from plough- 

 ing, by which the mould would be more extensive- 

 ly exposed to the influence of the air, and would 

 thus much sooner undergo those chemical chang- 

 es, on which the subsequent fertility is in a great 

 measure dependent. 



There is no reason which should lead one to 

 suppose that plaster can increase the tor.iperature 

 of a decomposing or decompose-1 vonetable mass ; 

 for as the heat generated in this process arises 

 from fermentation and this again from chemical 

 changes in the nature of the mateTiiiis, the sul- 

 phate of lime must itself undergo some change or 

 •some decomposition to add to the fermentative 

 matter and thus to angment its temperature. But, 

 so far as we know, neither vegetable nor perhaps 

 animal matter contains any thing which in the cir- 

 cumstances, in which they are placed, is capable 



