330 



NA TURE 



[August 4, 1892 



acid act one on another to form elhyl-sulphuric or sulphovinic 

 acid : — 



SO2H02 + EtHo = SOjHoEto + OH2 

 but when ethyl-sulphuric acid is heated with alcohol, ether is 

 formed with the reproduction of sulphuric acid — 



SOjHoEto + EtHo = OEtj + SOoHoj 

 the sulphuric aci 1 is then able to produce ethyl-sulphuric acid by 

 acting on more alcohol, so a continuous proJuction of ether and 

 water takes place without loss of sulphuric acid. Another well- 

 known action is the combination of oxygen and hydrogen under 

 the influence of spongy platinum. In this case the platinum 

 remains apparently unaltered, and is capable of causing the com- 

 bination of any quantity of mixed gases. As spongy platinum 

 possesses the power of absorbing large quantities of gases, it is 

 usually said that the molecules of oxygen and hydrogen are so 

 much condensed in the plaiinum that they are brought within 

 the sphere of one another's attractions, and consequently 

 combine. 



Another instance of an action of this kind is afibrded by the 

 oxidation of ammonia in the presence of chromic oxide. When 

 amnionic dichromate is heated an evolution of gas occurs, and a 

 residue of chromic oxide is left which bears a striking 

 resemblance to a mixture of black and green tea ; when 

 some of this substance is placed on a piece of 

 wire gauze, heated and then supported over a vessel 

 containing a strong solution of ammonia, the oxide glows in a 

 mai)ner similar to the glowing of spongy platinum under the 

 influence of a mixture of hydrogen and air. Under these con- 

 ditions the chromic oxide facilitates the oxidation of the am- 

 monia, but it becomes changed during the process ; instead of 

 having the appearance above described, it acquires a bright 

 green colour. Now, we know that chromium is capable of 

 forming several combinations with oxygen. Is it therefore too 

 much to suppose that the chromium is alternately oxidized by 

 the oxygen of the air, and reduced by the hydrogen of the am- 

 monia, so that, although in the end it has the same composition 

 as at the beginning, nevertheless it has been continuously de- 

 composed and reproduced ? Now, may not a similar change 

 take place during the action of spongy platinum on a mixture of 

 hydrogen and oxygen ? The alteration of the platinum is very 

 slight, but I believe I have observed a slight modification of the 

 appearance of a fragment of spongy platinum that was kept 

 glowing by a small jet of purified hydrogen for some hours ; the 

 gas not being allowed to burn so as to heat the platinum to a 

 very high temperature, the metal appears to be compacted and 

 to be covered by minute spherules of glistening metal. Now, 

 may not the platinum have entered into combination with one 

 or other of the gases and been subsequently reduced ? If this is 

 the true explanation, then we have in this case a continuous 

 series of chemical changes and the "catalysis" is explained. 



We all know the ease with which oxygen is obtained from 

 potassic chlorate when heated with a small quantity of oxide of 

 manganese ; the quantity of peroxide is the same at the end of 

 the process as at the beginning, and it may be used over and 

 over again to assist in the decomposition of fresh potassic 

 chlorate. The oxide of manganese undergoes a molecular 

 alteration ; if a crystalline variety is employed, it is found, at 

 the end of the process, to have been transformed into fine 

 powder. 



I hope I have proved to the satisfaction of my brother 

 chemists that potassic permanganate is first formed and subse- 

 quently decomposed with the reproduction of manganese per- 

 oxide. 



Oxide of cobalt possesses the remarkable property of decom- 

 posing solutions of hypochlorites at moderate temperatures with 

 evolution of oxygen. For some time I have been endeavouring 

 to find the explanation of the change, but hitherto without com- 

 plete success. At first it seemed probable that an unstable 

 cobaltate, analogous to a feirate, was formed and decomposed 

 at the temperature of the experiment. In fact oxygen is evolved 

 when chlorine is passed through a boiling solution of sodic 

 hydrate containing ferric hydrate in suspension. But no evi- 

 dence of the existence of a cobaltate could be found. When a 

 cobaltous salt is added to an alkaline solution of a hypochlorite, 

 a black precipitate is formed which is usually stated to be cobal- 

 tic hydrate, CogHog, but Vortmann has shown that, when a 

 cobaltous salt is mixed with a solution of iodine in potassic 

 iodide, and the liquid rendered alkaline by sodic hydrate, the 

 precipitate formed at a temperature between 50° and 60° ap- 



NO. II 88, VOL. 46] 



proaches in composition the dioxide of cobalt, CoOj. He also 

 found that the precipitate lost oxygen at the temperature of boil- 

 ing water. I have repeated some of his experiments and can 

 quite confirm them, although I have not obtained an oxide con-, 

 taining quite as much oxygen as his richest oxide. The oxides 

 I prepared rapidly effected the decomposition of a solution of 

 sodic hypochlorite, and that without undergoing any loss of 

 oxygen themselves ; in fact, in the two experiments made, the 

 cobalt compound contained a little more oxygen after boiling 

 with the hypochlorite. 



We have now many instances of the influence which small 

 quantities of substances have upon chemical reactions. These 

 influences may be more common than is generally supposed. 

 The presence of a third body is frequently helpful in the combi- 

 nation of elements with one another : thus dry chlorine will not 

 attack melted sodium or finely divided copper ; an electric 

 spark will not cause a dry mixture of carbonic oxide and 

 oxygen to explode ; carbon, phosphorus, and sulphur will 

 not unite with dry oxygen, and as chemical science progresses 

 we may find that many well-known actions are conditioned by 

 the presence of minute traces of other matter which have hither- 

 to escaped detection. We all know the profound alterations of 

 the properties of substances by minute traces of impurities ; le.ss 

 than one-tenth per cent, of phosphorus will render steel unfit 

 for certain purposes. The sapphire and ruby only differ from 

 colourless alumina by the presence of traces of impurities hardly 

 recognisable by chemical analysis. During this meeting we 

 hope to have a contribution to the section on the influence 

 of minute traces of what may be called impurities on the pro- 

 perties of different substances and their influence on chemical 

 changes. 



In this city, where the first public chemical laboratory was 

 started in 1823, by Dr, Anderson, the assistant of Prof. Hope, 

 it is hardly necessary to insist on the extreme importance of 

 teaching chemistry by practical work, but unfortunately, even 

 at the present time, endeavours are made to teach the subject by 

 means of lectures (sometimes without experiments) or by read- 

 ing. Those who are acquainted with chemistry well know the 

 impossibility (this is hardly too strong a word) of learning the 

 science, especially in the first stages, without actual experiment, 

 by which a practical acquaintance with chemical phenomena is 

 obtained. The attempt to learn chemistry without practical 

 experience reminds one of the well-known story (for the truth 

 of which I will not vouch) of a mathematician who lectured 

 on natural philosophy ; he was visiting a foreign laboratory, and 

 stopped before a piece of apparatus and asked what it was : on 

 being told it was an air-pump, he exclaimed, "Dear me! I 

 have lectured on the air-pump for twenty-five years, and this is 

 the first time I have seen one." It is problematical if his 

 students can have derived much advantage from his lectures. 

 Teaching of the kind to which reference has just been made is 

 generally given to candidates for examinations who do not intend 

 to take up chemistry as their chief subject. At the present time 

 chemistry is required for entrance and preliminary examinations 

 from many classes of students. There is no doubt that it is an 

 excellent means of education, teaching a boy to observe and 

 draw conclusions from his observations ; but if he makes no 

 observations it is little more than useless cram, the memory 

 might as well be exercised by learning a novel by heart. 



This imperfect mode of teaching chemistry arises principally 

 from the difficulty of obtaining properly appointed laboratories 

 in schools, in addition to which the very strong fumes are some- 

 times disagreeable, making it inconvenient to have them in or 

 near a house, to say nothing of the possible dangers to the 

 clothes and their contents ; but there is no help for it, the teach- 

 ing must be accompanied by experimental demonstration, as 

 was indicated in the Reports on the teaching of chemistry which 

 have been presented to this Association in former years. It 

 must be admitted that examinations do not always discover the 

 best student ; many are capable of preparing for examinations 

 with a small knowledge ot their subject, others, with a good 

 knowledge, fail from nervousness or other causes, but at the 

 present time examination, though far from perfect, is almost the 

 only means we have of judging the fitness of the candidate. By 

 properly selecting questions the examiner may, to a considerable 

 extent, discourage cram ; he should endeavour to find cut what 

 the pupils have actually seen, and to make them draw conclu- 

 sions from facts which they have either themselves observed, or 

 which have been described to them ; it is only in this manner 

 that chemistry can be used as a n.eans of mental training. 



