368 



NATURE 



^August 1 8, 1887 



leaves. The first-named has, as you know, large dark 

 purple flower spikes of 2 feet long ; the other, on the 

 other hand, only short spikes with small white flowers. 

 On these Coccolabas are found several nice Epi- 

 dendrums. 



The savannahs are frequent and extensive here, and 

 afford a number of smaller plants of various descriptions. 



In several parts of the island there are tracts of 

 mahogany, which are cut for export. 



The climate is generally cooler than in the smaller 

 islands. I found the nights quite fresh. In the higher 

 mountains, of course, it was quite cold at night. On the 

 Pico del Valle I passed one night. We had a large fire 

 blazing all night ; in the morning, at 6 o'clock, the thermo- 

 meter only showed 1 1° C. 



Rivers and brooks are innumerable, but on account of 

 the freshets and the violent current after rain, hardly 

 any aquatic plants are seen, at least in this part of the 

 island. I missed the beautiful Pontedera of Porto Rico. 



I send you to-day, by mail, seeds of the only palm 

 which I have been able to obtain, a species of Etcterpe, 

 which is common here above 1200 feet, and the fruit of 

 which is much eaten by half-wild hogs. It is called 

 " Manacla" here, and grows to a height of about 30 to 40 

 feet. 



Towards the end of the year I propose continuing my 

 explorations of the West Indies, having in view a further 

 investigation of this island, especially of the east and 

 south, and furthermore of the Bahamas (especially 

 Andros) and the two islands of Tobago and Grenada, 

 both of which, I believe, are very little explored. The 

 northern part of Dominica is also still terra incognita^ 

 unless something has been done there since my visit in 

 1879 ^rid 1 880. This island is particularly interesting to 

 me. I believe it is one of the most luxuriant of the West 

 India Islands. 



CONSTITUTIONAL FORMULA AND THE 

 PROGRESS OF ORGANIC CHEMISTRY. 



T F the mere increase in the number of known facts were 

 ■*• an accurate measure of the growth of a science, the 

 question as to the progress of organic chemistry would be 

 easily answered. Let the reader open a text-book on 

 chemistry of fifty or sixty years ago, and he will find, 

 sheltering itself under the wing of the inorganic chemistry 

 of that day, the half-fledged science of organic chemistry. 

 Then let him turn to Beilstein's gigantic Handbuch der 

 organischen Cheinie, with its more than two thousand large 

 closely-printed pages — a mere classified catalogue of the 

 known facts, written moreover in the highly-condensed 

 elliptical style appropriate to catalogues. Here is in- 

 ciease. 



But life is not measured by days, nor chemistry by new 

 compounds ; and the reader might resent the invitation to 

 appraise the progress of organic chemistry by this rough 

 quantitative method. A qualitative analysis is necessary 

 here. 



But how ? The really important facts, even with the 

 aid of the most judicious selection, could hardly be packed 

 within the compass of a single article ; nor would they be 

 interesting, or, in such compression, even intelligible, to 

 the non chemist. There are of course the usual pieces de re- 

 sistance in the shape of the coal-tar colours, and the various 

 naturally-occurring compounds that have been artificially 

 prepared ; but probably the general reader has heard 

 enough of these already, and might feel inclined to ask 

 whether organic chemistry has nothing further to say for 

 itself. 



There is, however, a peculiarity of organic chemistry 

 which distinguishes it from the remainder of the science. 

 The aim of all chemistry is to ascertain the constitution 

 of matter, and the said peculiarity of organic chemistry is 



that it expresses its views on this important subject 

 greater detail, more precisely (or, as some will have 

 more dogmatically), than inorganic chemistry. Its artici 

 of belief on this head are embodied in its constitution 

 formulae. 



Here we touch on matter which every chemist will 

 once recognize as debatable. But, for good or for ev 

 these constitutional formulae are, apart of course fro: 

 the dry facts, the main scientific outcome of organ 

 chemistry : they form the particular contribution whic 

 organic chemistry has been able to make towards solvir 

 the central problem of all chemistry — the constitution 1 

 matter. At present they crown the edifice of organ 

 chemistry. Are they the keystone of an arch, or a mei 

 meaningless architectural embellishment ? This is tl: 

 most general question which organic chemistry can put t 

 itself at the present moment, and an attempt to answer 

 is the most fitting mode of reviewing the past work of th 

 science. Let us therefore turn our attention to thes 

 constitutional formulae, and ask ourselves what they are 

 what their meaning is, their scope, their justification. 



According to some unfriendly critics, constitution; 

 formulae have done incalculable harm to chemistry b 

 causing chemists to desert accurate experiment an 

 observation for idle speculation — to substitute for th 

 arduous work of the laboratory the easy task of stringin 

 together atomic symbols, according to certain rules, o 

 paper. There may in some cases have been soms sma 

 measure of truth in this accusation^n other words, ther 

 may have been some occasional abuse of constitution 

 formute ; but the injustice of the accusation as a whol 

 is sufficiently proved by the fact that the most sue 

 cessful experimenters of the day in the domain of organi 

 chemistry are enthusiastic supporters of constitutions 

 formulas, and confess to having been guided ]jy thes 

 formulse at almost every step of their researches. Thi 

 actively-hostile attitude towards constitutional formulae i 

 fortunately becoming daily rarer. 



Another class, not of detractors, but of rather lukewarr 

 friends, of the constitutional formula, regard it as a con 

 venient mnemonic device, by the aid of which the com 

 position of otherwise hopelessly complex compounds ma; 

 be successfully impressed on the memory. It is perfectl; 

 true that constitutional formulae do perform this importan 

 function ; but an impartial review of the case will, wi 

 imagine, lead to their being rated somewhat more highly 

 than this. 



A third class may be described as the undiscriminatint 

 admirers — the injudicious friends — of the constitutiona 

 formula. To them the constitutional formula is a fina 

 expression of the position of the atoms in the molecule— 

 a picture of the molecule itself. This is a phase of belie 

 which many pass through in making their first acquaint 

 ance with organic chemistry, and its existence is due t< 

 the circumstance either that the teacher is so mucl 

 engrossed in impressing the complex array of facts anc 

 theories upon the mind of the student that he has no 

 time to introduce philosophic limitations and doubts, 

 that he considers such an addition only calculated ti 

 render an already somewhat tough intellectual fare totall , 

 indigestible by a beginner. However this maybe,,'"" 

 certain that the faith of the beginner is quite as freque 

 appealed to as his reason. 



We shall best be in a position to discern the meaij 

 and to estimate the value of these constitutional form| 

 if we consider to what necessity they owe their or 

 and how far they fulfil the purpose for which they \^ 

 devised. 



The atomic theory, as propounded by Dalton, satisfic^ 

 for a time the requirements of chemists. For e^ 

 properly-analyzed compound a more or less simple ate 

 proportion could be calculated, and this atomic proj 

 tion was expressed in the empirical formula of the cjj 

 pound. These empirical formulae were combined 



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