128 



THE GARDENERS' CHRONICLE. 



[August 4, 18*8. 



THE CHEMISTEY OF VEGETA- 

 TION, IN REFERENCE TO THE 

 GROWTH OF THE POTATO. 



(Continued from p. 910 

 Historical Summary. — Whatever may be said 

 in favour of the different " methods " adopted in 

 different text-books as a help to "learning che- 

 mistry " for professional or technical purposes, the 

 historic method has this advantage for the student 

 of plant life, that it at once brings him in contact 

 with the earliest investigations of compounds 

 of C H ON (Carbon, Hydrogen, Oxygen, Nitrogen). 

 From these investigations all our modern chemistry 

 has a direct descent, the explanations of phenomena 

 having come in more or less clearly from electri- 

 cians and physicists, till perhaps the earlier workers 

 would not fully recognise their science. From 

 C H N the greater part of the physical basis of 

 plant structure is built up, and it is to certain com- 

 pounds of these on which anyone who studies plant 

 life has mainly to fix his attention. 



The study of " ash " or that which remains after the 

 combustion of a plant, and methods of analysis bring 

 him in contact with other elements and their com- 

 pounds, but still with the greater part of the know- 

 ledge set forth in handbooks of the science, he has 

 no directly practical interest. Nor need he fear that 

 he will fail to understand how we have come to know 

 what we know if he does not carry his historic retro- 

 spect further back than the middle of the last 

 century. It is true that some have claimed both for 

 Boyle (b. 1627), and for Hales (b. 1677), a high 

 place as pioneers in chemistry. That may arise 

 from modern interpretations put on their writings. 

 It at least is difficult to trace any direct continuity 

 of the influence of their researches on their suc- 

 cessors. 



Black's Work — Caebonic Acid. 



Two important changes in chemical work which 

 signally characterised the early part of the second 

 half of the last century, were the re-introduction of 

 the balance, and the commencement of the study of 

 gases. Till then air was to chemists simply air, and 

 the few gases (as we now call them) that had been 

 examined were regarded as " tainted air." There is 

 no trace that any one even used the word airs* in 

 the plural till Black did, and from the days of 

 Alhazen (a.d. 1100) the balance seems to have been en- 

 tirely neglected by chemists till Black again used it. 



The old Greeks fond of, and ingenious at, 

 guessing at the origin of things, had in turn held 

 that earth, water, air, and fire, were the 

 " elements " from which things sprung, and these 

 had continued to be regarded as elements. 



The mediaeval chemists had principally paid atten- 

 tion to the qualities of bodies, their action on one 

 another, and as drugs. Quantity they disregarded, 

 and hence could never have arrived at a notion of 

 the proportions in which bodies influence one 

 another. 



Prior to Black's time, the explanation of combus- 

 tion (put forward by Beecher and Stahl about sixty 

 years previously) was that, when a body burned, 

 there was something that passed out of it into the 

 air. This hypothetical something was named 

 phlogiston {$Aoyio-Tov — burnt), and "the phlogiston 

 theory " was believed in by everybody — by what is 

 called " all the world," and, I suppose, " his wife " too. 

 We know that some years later one wife — Madame 

 Lavoisier — after her husband had "abjured the 

 heresy," took prominent part as a widow in the 

 ceremony of burning the " wicked books." 



Black's discovery was a simple one, but a memor- 

 able one. His experiment is worth while repeating 

 by those who have not yet done so. Most people 

 know that burnt lime is caustic. Those who do not 

 know this can get the information from any 

 bricklayer. Blackt when about twenty years of 



* Van Helmont (b. at Brussels 1577) appears to have been 

 the first to use the word gaz in the sense in which we use gas. 



t The exact year is uncertain, and so is the date of the first 

 publication of his paper. As no question of priority isinvolved 

 it is not of importance. 



age (1752) was examining the difference between 

 mild lime and caustic lime. It occurred to him to 

 try whether the phlogiston supposed to give it its 

 causticity when it enters into it from the burning 

 fire made it much heavier. He weighed a lump, 

 burnt it, and then weighed it again. Instead of being 

 heavier it was lighter. He left the lump on the 

 balance, apparently attending to something else when 

 he had noted the weight. Some time after, going 

 to his balance again he found the lump nearly its 

 original weight. This set him thinking. Evidently 

 in burning, something had gone out of it into the 

 air, and the regain of the weight was due to some- 

 thing that came in from the air. He then poured acid 

 on limestone. Again he found something went out, 

 for even with the additional weight of the acid, his 

 lump became lighter, and again, on standing, the 

 weight in time was regained, showing something came 

 in from the air. As his attention was directed mainly 

 to the cause of the causticity of lime, and he was at 

 Edinburgh preparing for his M.D., he did not at the 

 time push his enquiries further concerning this " air " 

 than to identify it with the air we breathe out. It 

 for many years was known by the name " fixed air." 

 Although chemists now call it carbon di-oxide, it 

 still retains in popular language its more familiar 

 name, carbonic acid. The fact of its composition 

 being 



© 

 ©0 



and the adoption of the symbol C O s was of course 

 not till after Dalton's law of multiple proportions 

 was established. We owe to Lavoisier the first ex- 

 planation of its composition. 



The important part it plays in relation to plant 

 life was not understood till later still.* 



Cavendish— Hydrogen, &c. 



Cavendish, who at the age of twenty-two had left 

 Cambridge shortly before Black's dissertation waspub- 

 lished, took up among other subjects an examination 

 of the " fixed air" with a view to determine its density 

 as compared with ordinary air. His rigid rule in all 

 his work was to measure, weigh, and calculate. His 

 habits of exactness and method extended to his own 

 daily life, of which some amusing accounts are given 

 in his memoirs by Dr. Wilson. t In 1760 he joined 

 the Royal Society, and in 1766 contributed his first 

 three papers under the title " Experiments on Facti- 

 tious Airs." They were printed in the Transactions 

 of the Society for that year, vol. Ivi., p . 141. 



The plate given to illustrate what he terms his 

 " contrivance " — for he does not use the more dignified 

 word apparatus — is well worth looking at, it is so 

 charmingly primitive and simple.f. The pneumatic 



* It is difficult to determine how far Boyle or Hales under- 

 stood it. t Cavendish Society's publications. 



I The kind of way in which Cavendish worked can be readily 

 understood by an experiment with homely apparatus. Take a 

 glass jam or pickle jar. Pour in half a pint of water and make 

 a mark (say a file scratch) where the water stands. Pour in 

 another half pint and mark that, then another and another. 

 Put the jar into a tub of water deep enough to fill the jar, then 

 holding it, mouth downwards, gradually raise it till it is nearly 

 out of the water. It can be easily supported in this position 

 on the edges of two bricks. Blow through a tube with its end 

 held close under the mouth, and as the bubbles rise the water 

 in the jar will be gradually displaced. In this way you can 

 collect a half pint, pint, &c, of the carbonic acid you have 

 breathed out. A little more trouble will illustrate the method 

 of collecting gases generated from different sources, Take 

 another jar with a well-fitting cork, into the cork insert a 

 bent tube long enough to reach over the tub to the mouth of 

 the jar in the water. Put some effervescing powder and 

 water in the jar, put in the cork and place the end of the tube 

 under the mouth of the inverted jar. You will be able (roughly) 

 to measure the amount of gas given off from the effervescing 

 mixture. 



This will illustrate the meaning of the expression " ga*es 

 collected over water." As some gases are very soluble in water 

 mercury is used instead. Then gases are " collected over 

 mercury." In this way a certain volume (say half a pint) of 

 one gas can be mixed with double that volume of another by 

 letting in first the one and then the other. This Cavendish 

 di I with hydrogen and air, and afterwards with hydrogen and 

 oxygen, and " exploded " the mixture by applying a light. In 

 delicate researches accurately gradulated tubes are used in- 

 stead of roughly scratched pickle jars, but the method is 

 practically the same. 



trough with its convenient shelf had not been in- 

 vented. That isbelieved to have been Priestley's device. 

 The phials that were to collect his " airs " were, after 

 Hale's fashion, hung mouth downwards in water by 

 strings. What would a student accustomed to a well- 

 equipped laboratory think of such "contrivances"? 

 Yet he gives a most exact description to even the 

 "luting" of the stoppers, and the joinings of the 

 glass tubing. The three papers were on : — 



1. The specific gravity of inflammable air from 

 five different sources (now called hydrogen). His 

 result was that it is but one-eleventh of common air. 

 He noted that inflammable air cannot burn without 

 the aid of common air. 



2. The specific gravity of fixed air (now commonly 

 called carbonic acid). His result was that it exceeds 

 that of common air by one-half. 



3. On the air produced by fermentation. 

 Engaged with other work, Cavendish did not 



communicate any other chemical paper till 1784. 



RuTHEEFOED NlTBOGEN. 



Meanwhile, Rutherford, in 1772, made known the 

 existence of another distinct kind of air in the 

 atmosphere. Mice could not breathe in it : hence the 

 inference that it had nothing to do with supporting 

 life like " common air." It would not support com- 

 bustion. Though fixed air also would neither support 

 life nor combustion, this air was not identical with 

 it. It was called phlogisticated air,* or, as an alter- 

 native azot or azote (a, privative, and sbtikos, belong- 

 ing to life). Its modern name is nitrogen. Priestley, 

 not knowing of Rutherford's work, also found it a 

 little later, and for this he received the Copley 

 Medal of the Royal Society. 



It seems to us strange from our standpoint that 

 though when phlogisticated air was "discovered" by 

 Rutherford twenty years had elapsed since Black 

 found " fixed air," yet the " air " which supports life 

 and combustion (the "air" or "gas" we now call 

 oxygen) was unknown. W. 8. M. 

 (To be continued.) 



URSERY NOTES. 



COOMBE WOOD. 



(Continued from p. 94 J 



Clerodendron trichotomum is a pretty white- 

 flowered species, useful to the gardener at this season 

 for greenhouse decoration ; but the plant as usually 

 grown has the drawback of flowering only when it is 

 several years old, and therefore compelling the gar- 

 dener to have relays of plants if he would have 

 some of them in flower year by year. Mr. Howard, 

 the manager at Coombe Wood, gets over this diffi- 

 culty by grafting young wood on old stocks of the same 

 species, which then flowers the next year afterwards. 



The white Escallonia Philipiana (Gardeners' 

 Chronicle, July 27, 1878, with figure) was full of 

 flowers, just going off in the middle of July. It is 

 quite hardy, standing without protection in the 

 border. The flowers are white, very numerous, and 

 sweetly scented. Close by the above plant was a 

 great bushy Japan Oak, Quercus Burgeri (acuta). It 

 too is hardy, and possesses fine large evergreen 

 foliage. Although seen here as a bush, it will, with 

 timely pruning, form a stemmed tree. 



Osmanthus myrtifolius is another small growing, 

 quite hardy evergreen bush that would bear annual 

 cutting, and would be well adapted for a garden 

 hedge plant, or to take a place amongst formally 

 kept specimen shrubs. 



An ornamental standard, deciduous, small tree is 

 found in Cerasus Juliana rosea, excellent for a 

 sheltered position in a lawn. In Ornus brachypoda 

 is found a Japanse representative of our flowering or 

 Manna Ash. The foliage is larger, if anything, 

 than the more common Ornus, and its hardiness 

 undeniable. Of Japanese Acer many were noticed — 

 thrifty plants of some years standing, therefore of 

 great hardiness. It must be from some notion which 



* Air phlogisticated was distinct from phlogisticated air. 



