TRANSACTIONS OF SECTION B. 669 



of manganese undergoes a molecular alteration ; if a crystalline variety is employed, 

 it is found, at the end of the proces;*, to have teen transformed into line powder. 



I hope I have proved to the satisfaction of my brother chemists that potassic 

 permanganate is first formed and subsequently decomposed with the reproduction 

 of manganese peroxide. 



Oxide of cobalt possesses the remarkable property of decomposing solutions of 

 hypochlorites at moderate temperatures with evolution of oxygen. For some time 

 Ihave been endeavouring to tind the explanation of the change, but hitherto with- 

 out complete success. At iirst it seemed probable that an unstable cobaltate, 

 aualogous to a ferrate, was formed and decomposed at the temperature of the ex- 

 periment. In fact, oxygen is evolved when chlorine is passed through a boiling 

 solution of sodic hydrate containing ferric hydrate in suspension. But no evidence 

 I if the existence of a cobaltate could be found. When a cobaltous salt is added to 

 un alkaline solution of a hypochlorite a black precipitate is formed which is usually 

 stated to be cobaltic hydrate, COoHOg, but Vortmann has shown that, when a 

 cobaltous salt is mixed with a solution of iodine in potassic iodide, and the liquid 

 Tendered alkaline by sodic hydrate, the precipitate formed at a temperature between 

 50° and 60° approaches in composition the dioxide of cobalt, CoO.,. He also found 

 that the precipitate lost oxygen at the temperature of boiling water. I have 

 repeated some of his experiments, and can quite confirm them, although I have not 

 obtained an oxide containing quite as much oxygen as his richest oxide. The 

 oxides I prepared rapidly effected the decomposition of a solution of sodic hypo- 

 chlorite, and that without undergoing any loss of oxygen themselves ; in fact, iu the 

 two experiments made the cobalt compound contained a little more oxygen after 

 boiling with the hypochlorite. 



AN'e have now many instances of the influence which small quantities of sub- 

 stances 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 

 combination 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 hitherto escaped detection. We all know the profound altera- 

 tions of the properties of substances by minute traces of impurities ; less 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 properties of diilerent substances and their 

 influence on chemical changes. 



In this city, where the first public chemical laboratory was started in 182.3 by 

 Dr. Anderson, the assistant of Professor 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 reading. Those who are ac- 

 quainted with chemistry well know the impossibility (this is hardly too strong a 

 word) of learning the science, especially in the first stages, without actual experi- 

 ment, by which a practical acquaintance wi'^h 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 



