M. RAFAELLE YIlEIA ON POPU'LISI 111.-On the variation in the relative proportion of Polash and Soda present in certain samples oJ Barley grown in plots of ground arttjiicially irnpregnated with one or' other of these Alkalies. BY CHARLESDAUBENY, M.D. F.R.S. PRESIDENT OF THE CHEMICAL SOCIETY OF LONDON. Although the necessity for a due supply of earthy and alkaliiie matters to the growing vegetable may be at present regarded as indisputable a good deal still remains to be done before we can pre- tend to lay do~vii,with any degree of certainty the extent to which any one of those ingredients commonly present in a particular plant may be replaced by others without affecting its health or develop-ment. Saussure,* indeed had long ago ascertained that a tree varied * Recherches sur la vCgCtation 1804.DR. DAUBENY ON THE VARIATION 1N in its mineral constitution according to the nature of the soil in which it had grown; a fir for instance taken from a felspathic rock being found by him to contain much potash but no magnesia; whilst the same from a dolomitic rock was charged with magnesia but exhibited a proportionate deficiency in alkali. Bert hier,* also had afterwards confirmed this inference by his analysis of two samples of oak timber the one obtained from Norway the other from Allevard in Dauphinp as the proportion of soda and of potash was found by him greater in the former instance than in the latter. The independent results of these trustworthy chemists Liebigt has endeavoured to bring under the operation of a general law which he has himself suggested in showing that the SUM of the oxygen present in all the samples of timber analyzed whether by Saussure or by Bcrthier was uiiiformly the same however much in relative amount the bases theniselves might vary.This remarkable observa- tion would certainly seem to favour the idea that provided there be bases present in the soil sufficient for neutralizing the organic or mineral acids generated or secreted by the growing vegetable the nature of the former was comparatively unimportant; and thus might lead us to conjecture that isomorphous bodies at least which replace each other in the structure of a mineral might do the same also in the organization of a plant. Amongst other facts tending to the same conclusion may be cited the analyses made some years ago by Will and Fresenius of barley grown in the interior of Germany and in the more maritime districts of the Netherlands as the former was found to contain a smaller proportion of soda in comparison with the potash present than the latter.Rut before we allow ourselves to push our inferences beyond the point to which the above facts strictly warrant us in proceeding let us consider for a moment the arguments that may be adduced on the opposite side as tending to show that a certain definite mineral composition is to be ascribed to each particular plant and probably even to every one of the several organs of which it is made up. If the nature of the mineral ingredients present in a plant were a matter of indifference provided only the neutralizing power pos- sessed by thein were sufficient for the purpose of enabling them to combine with the acids present; or even if without proceeding to this extent we suppose one alkali capable in general of supplying * Ann.Ch. Phys. [S] LSXXII. 1-Chemistry in its application to agriculture &c. THE PROPORTION OF POTASH AND SODA IN BARLEY. the place of another or an alkaline earth of being substituted for an alkali what then is the end of that remarkable power of selection which all plants possess and which is so remarkably evinced by those of marine origin in their assimilation not only of iodine but also of potash from a sea containing both in infinitesimal proportions only.The case of the Algs indeed is only an extreme example of a generally pervading law; for it is sufficient to cast a glance over any series of vegetable analyses as for instance the tabular view given by Dr. Karl Bischof in a late number of the “Journal fur praktischc Chemie,”* of the composition of various plants to be convinced that they in general absorb potash in preference to and even to the exclusion of soda without refereace to the comparative abundance of the two alkalies in the soil. Dr. Bischof shows that out of a series of 200 ash analyses of land plants or of particular portions of them there are more than gths in which the proportion of potash was estimated to exceed that of soda and more than +th in which potash alone was found these latter analyses moreover being the most reccnt and probably therefore the most trustworthy.On the other hand there is not a single plant known in which soda alone occnrs and only a few excepting those belonging to the class of marine algs in which its amount exceeds that of potash. Bischof also assigns reasons for supposing that the propor- tion of soda in the ashes may often have been over-estimated. It seems moreover difficult to understand why if soda can takc the place of potash and lime or magnesia of either the same should not be the case with strontia; and yet I found several years ago,? that when a plant had been watered with a solution containing that earth SO minute a trace of it was found in its ashes that it became impossible to suppose the principle in question to have entered into the com-position of its tissue.Lastly with reference to the resnlts obtained by Will and Fresenius I may be permitted perhaps to set against them some made a few years ago in my own laboratory which tended to show that barley possessed the same mineral com- position so far as its alkalies were concerned whether it had been grown in the east or west coasts of England or in the more central district of Oxfordshire. $ Deeming therefore the subject to be one open to further investi- gation I was induced last summer to institute a few experiments; * Yol. SLVII. -t Linnean Trans. 1833. t Bakerian Imtiire on the rotation of crops in the Ph. Trans. for 1845 DR. DAUBENY ON THE VARIATION IN the results of which I will next submit as introductory to a statement of certain views respecting the mode in which the two alkalies come to be formed in the ashes of a plant and the functions severally discharged by them in their living organisation which I am desirous of laying before this Society.For the purpose of ascertaining how far the alkaline constitution of a crop of barley might be modified by a difference in the quality of the soil in which it was grown 1 selected in the same part of thc Oxford Botanic Garden seven plots of ground of equal size and as nearly as possible similar in point of quality exposure &c. Two of these plots were manured with a pretty strong dressing of sub- carbonate of potash ; two with an equivalent amount of subcarbonate of soda; two with common salt in quantity sufficient to snpply the same proportion of soda as the last; whilst the seventh was lcft without any application at all.The size of thc plots was such that the quantity of potash added would be equivalent to about ten bushels of common salt to the acre and to corresponding quantities of carbonate of soda and of carbonate of potash to the same surface of soil.+ In order to prevent these saline matters from being too speedily washed away by rain I had previously dissolved them in water and had mixed each of the several solutions with a bulk of stiff clay large enough to absorb the whole of the liquid. The mixture was then exposed to the sun and air in order that the salts might become dry and be thoroughly incorporated with the mass ; after which the whole was thrown upon the plots intended for their reception and mixed up intimately with the soil down to the depth of two feet from its surface.An equal amount of barley was then sown in each of the said plots and the crop obtained separately dried and weighed the straw and grain having been kept distinct. A portion of each having been then incinerated the soluble portion of the ash was taken up by water after which everything except the alkaline salts was removed by the methods usually employed for that purpose. An aliquot portion of the alkaline residuum was in each case converted into chloride and the potash separated from the soda-salt by means of the chloride of platinum.* The qnantities being respectively 7 lbs. of pearl-ash 20 , of subcarbonate of soda in crystals 9 , of common salt to each plot these numbers representing equivalent arn0unt.s of the two alkalies. THE PROPORTlON OF POTASH AND SODA IN BARLEY. The following were the results obtained by this method PLOTS yielded Maiiured with j n 100 parts of altogether. of the alltaline residuum. I I i Potash. Soda. grain 138 111s. 84.50 15.50 Carbonate of potash . { avgfc:fptshe } 718 11)s. Irk.{ straP; 58 , 79.50 20.50 grain 13) 1y 76.50 23.50 Carbonate of soda .{ , , 71 ,) viz. { straw 574 7y 72.75 27-25 grain 143 , 76.50 23.50 Chloride of sodium .{ 9p 7t 78 viz. { straw 63% ,) 76.50 23.50 -82.50 17.50 79.50 20.50 The difference between the amount of produce in the bed left unmanured and in the rest sufficiently attests the benefit that had been derived from every one of the saline matters added and that nearly in an equal ratio from each of them ; whilst the larger amount of soda present in the crops which had been dressed with carbonate of soda and with chloride of sodium might Seem toindicate that this alkaline principle had to a certain extent taken the place of the potash in consequence of its being present in the soil in a larger proportion here than in the other plots.But a little further consideration may perhaps suggest a different mode of explaining the facts in question. It must be recollected in the first place that the roots of plants suck up indiscriminately from the soil every kind of matter presented to them whether it be poisonous to them or nutritious as was long ago ascertained to be the case by Saussure.There must therefore be circulating through the system of a plant during all the stages of its growth a certain amount of every species of saline matter which happens to lie in contact with its roots of which although only that which is capable of being assimilated by its organs actually constitutes a part of its substance the remainder IS ncvertheless detained within the vegetable tissue for a certain time and cannot be separated from it by any known mechanical process. When therefore we dry a plant and reduce it to ashes,itsresiduum after incineration will contain not only the alkaline matter which actually entered into the composition of the organs themselves but likewise that circulating at the time through its tissue.The former DR. DAUBENY ON TILE VARIATlON IN indeed may be assumed to bear a constant relation to the volatilizable ingredients associated with it but the latter will necessarily vary according to the nature of the saline impregnation belonging to the water which bathes its roots. Thus from the soil to which nothing had been added a certain amount of soda as well as of potash would seem to have been extracted by the barley grown in it since both alkalies made their appearance in the portions incinerated. This however is easily explained inasmuch as by a previous analysis both soda and potash had been found to exist as original constituents of the soil.It is probable however that a good deal of the estimated quantity of each did not actually enter into the constitutioii of the organs but Bad been merely arrested in its progress through the plant so as to be present in it at the moment when the crop was cut down. From the addition of carbonate of potash to the soil only a small increase to the percentage of potashin the plant itself appears to have resulted; but it must be recollected that the quantity of potash present in the ground was distributed over a greater amount of crop as the produce of the beds rose in consequence of this addition from 63 to 719 lbs. By the dressing of carbonate of soda givcn to the third set of beds the percentage of soda was augmented in a still higher ratio because the increase of crop which followed did not in the same degree augment the consumption of soda by the plant as this alkali enters less abundantly into its actual organisation.A larger proportion of it therefore would remain in the juices circulating through the vegetable tissue and would therefore add to the apparent amount of soda in the crop when examined. The same explanation may apply to the increase of the same alkali which took place in the crop that had been manured with com- mon salt; this however would appear to exist in the plant as common salt since judging from the results of the analyses givcii in my Ualierian Lecture,* the salt in question entcrs as such into the tissue of a plant without undergoing decomposition.I may perhaps elucidate my meaning by the following hypothetical statenient in which the numbers given must be understood to be quite arbitrary and intended merely for the purpose of illustration. Confining ourselves to the grain of the barley experimented upon let us assume the normal quantity of potashand soda present in it to stand to cadi other in the relation of 74 of the fornier to 9 of the latter. * Phil. Trans. for 1845. THE PROPORTION OF POTASH AND SODA IN BARLEY. 15 Then in the unmanured crop Normal quantity being . . Potash 74.0 Soda 9.0 There will have been circu- lating through the crop when cut . . . . . , 8.5 , 8.5 or 50 to 50. .__ 82.5 17.5 In crops manured with carbonate of potash Normal quantity .. . . Potash 74.0 Soda 9.0 Circulating through the crop , 10.5 , 6.5 or 67 to 33. 84.5 15.5 In the crops manured with carbonate of soda and chloride of sodium Normal quantity . . . . Potash 74-0 Soda 9.0 Circulating through the crop , 2.5 , 14.5 or 15 to 85. 76.5 23.5 The above explanation may perhaps be open to objection; but I conceive it to be at least encumbered with fewer difficulties than would attend the notion of an actual substitution of soda for potash taking place within the organism of a plant; for in that case we must suppose that although a certain number of the atoms of the one alkali may be replaced by the other no such change can take place with regard to the greater part of those present; for were the latter possible that is were the whole or the greater part of the atoms of potash capablc of being replaced by soda not only would there have been a much greater difference in the constitution of barley grown in soils so largely impregnated as mine were with salts of soda in comparison with the same charged with those of potash ; but we should also be at a loss to explain the absence of a larger proportion of soda-salts in those samples of barley which I had ob- tained from the neighbourhood of the sea than existed in others taken from inland situations.In the experiments above detailed the utmost increase of soda in the crop caused by so liberal an application of soda-salts to the soil did not exceed 8 per cent of the whole; or in other words if wc adopt the hypothesis of substitution only 1atom in 12 of the potash actually present admitted of being replaced by soda nor does it 1G DR.DAUBENY ON POTASH AND SODA IN BARLEY. appear that the largest disproportion between the quantity of the two alkalies brought into contact with the plant can materially affect this limitation ; for otherwise marine algz which are nourished by a fluid in which the potash stands in the smallest possible relation to the soda could scarcely contain so large an amount of potash as is frequently found to cxist in them. And yet although we must in adopting this hypothesis assume certain limits to exist beyond which the usual constitution of a plant does not admit of change even by the most liberal supply of soda a large excess of this latter alkali must be supposed necessary in order that it should replace the potash in any degrec at all; inasmuch as we find no extraordinary amount of the mineral alkali in barley grown near the sea where soda-salts must be more abutidant than they are inland.These considerations would lead me to imagine that even in marine plants a portion of that large quantity of soda which is detected in their ashes may be derived from the juices circulating through their cellular structure and does not enter into their actual orga- nisation; so that even in them perhaps potash rnay turn out to be the alkali which plays the principal part iri building up the living fabric of the plant. I am by no means inclined however to limit the uses of the alkaline matter which is constantly contained in the sap to the one end of supplying a plant with the potash and soda which it requires for the formation of its different organs and for that of its characteristic secretions ; since Liebig himself has pointed out another function which both alkalies are equally fitted to dis- charge namely the fixation of carbonic acid through which owing to the consequent diminution of oxygen sundry other organic acids such as the tartaric the oxalic the inalic &c.rnay be formed. It is not my intention however to pursue this fertile subject on the present occasion ; in conclusion therefore I will only remark that I am fully aware of the scantiness of the data contributed by myself in this paper towards the elucidation of the question discussed in it; and that I should have been reluctant to occupy the time of this Society by bringing thcm forward had I not hoped that they might be the nieans of stimulating others of our members who have more leisure than myself for such investigations to undertake a larger and more precise train of experiments calculated to determine the still questionable point as to the power residing in plants to substitute one mineral ingredient for another in the construction of their respective organs or in the elaboration of the peculiar secre-tions which they contain.