5M 



SCIENTIFIC NEWS. 



[Nov. 16, 1888. 



If such yeast-water be coloured with extract of indigo, 

 this is decoloured more or less rapidly. A quarter of an 

 hour suffices in the most favourable cases. In a few 

 hours we may thus reduce 500 milligrams of dry extract 

 of indigo in 1 litre of liquid. This decolouration is so 

 much the more rapid as the microbia are more numerous. 

 On the other hand, heat and antiseptics such as phenol 

 (which kills the organisms) oppose the decolouration. 

 Filtration renders the filtrate inactive, whilst the liquid 

 remaining upon the filter retains its activity. The de- 

 colouration, therefore, is not the result of the action of a 

 substance previously generated by the microbia, which 

 would accumulate in the liquid, unless we suppose that 

 heat, antiseptics, and atmospheric oxygen introduced by 

 filtration destroy this substance — an inadmissible hypo- 

 thesis, since on saturating the unfiltered liquid with 

 oxygen we do not destroy the faculty of decolouration. 

 This power of the microbia is therefore an actual action, 

 direct or indirect, inherent in their life. It is a reductive 

 action, since the indigo resumes its colour on exposure 

 to the air, and the bacteria themselves are anaerobic. 



We must not confound this phenomenon with the de- 

 colouration of extract of indigo in an alkaline solution 

 of glucose, for in the latter case the microbia are not 

 necessary, and in the former the decolouration still takes 

 place in a neutral or slightly acid medium. It is not due 

 to hydrogen set at liberty, for its quantity is quite in- 

 sufficient to explain the result. 



This phenomenon is doubtless connected with the 

 special mode of respiration of these organisms. 



M. Duclaux has observed the decolouration by reduc- 

 tion of extract of indigo in milk, making its appearance 

 at the same time as the first organisms, and M. Dubois 

 has observed the spontaneous decolouration of litmus in 

 closed vessels, as due to a kind of micrococcus. 



It is not alone upon extract of indigo that these 

 microbia exert their activity by hydrogeneration. Log- 

 wood, orchil, saffranine are decolourised rapidly, though 

 less so than extract of indigo, and resume their colour 

 on exposure to air. Certain azo-colours, such as the 

 ponceau 3R of Meister, Lucius and Briining, the orange 

 No. 2 of Poirrier and Bordeaux red, are decolourised 

 rapidly, but do not recover their colour in the air. 

 Nicholson blue and imperial violet are decolourised in a 

 few days, but magenta, cochineal, and the colouring- 

 matter of wine resist for some weeks. Hence the 

 microbia in question may prove useful reagents for foreign 

 colouring-matters added to wine. 



&fejs;tract$ 

 of papers, flectut**, etc* 



SOCIETY OF ENGINEERS. 

 At a meeting of the Society of Engineers, held at West- 

 minster Town Hall on the 5th November, Mr. A. T. 

 Walmisley, President, in the chair, a paper was read on 

 "The Practice of Foundry Work," by Mr. H. Ross- 

 Hooper. 



The paper first briefly compared the particular quali- 

 ties and properties of pig iron, with the view of deter- 

 mining the varieties which are best adapted to the 

 requirements of the different kinds of castings made ; and 

 showing how the nature of cast-iron depended not only 

 upon the amount of carbon that it contained, but upon 



the conditions under which that carbon existed. The 

 author then proceeded to illustrate how, the failing of 

 portions of a cast-iron structure may be traced to a want 

 of knowledge in the way the lines of crystallisation flow 

 on the cooling of the metal, and mentioned the weak 

 points to be guarded against in the designing of cast-iron 

 work. Moulding or the production of a hollow mould to 

 receive the metal was next considered ; for to mould 

 melted iron into any required shape or form two things 

 are necessary — (1) a pattern of the article to be produced, 

 (2) a substance which will retain the impressions of the 

 pattern made upon it and resist the violence of the metal 

 when poured therein. To make a pattern a man requires 

 to be thoroughly conversant with the principles of mould- 

 ing, to so construct it that it may give a minimum ol 

 trouble to the moulder ; the materials used for pattern 

 making and the general essential points of this branch 

 being touched upon. The differences between green and 

 dry sand moulding, the requisites of a good foundry 

 sand, and the mode of preparing a mould for a small 

 girder bed-plate were entered into in detail, noticing 

 those particulars which should be observed in the con- 

 struction of sand moulding, and showing the uses of 

 cores and the method employed in their formation both 

 large and small. 



The author next proceeded to describe the features of 

 loam moulding, illustrating (by means of a working 

 model) the process of constructing a mould for a drum 

 capable of holding 200 feet of one-inch wire rope used in 

 the erection of the Sukkur Bridge, India. 



After explaining the operations of chill casting, malle- 

 able cast-iron, and the system of moulding known as 

 " Jobson's Blocks," whereby sand moulds of thin delicate 

 patterns can be made by ordinary labourers, the author 

 mentioned the different modes adapted for casting 

 according to the forms and requirements of the various 

 articles to be produced, and how sound results can only 

 be obtained by a careful attention paid to the feeding of 

 the metal to supply the shrinkage and drawing away 

 which must inevitably occur on the cooling of the metal. 

 The cupola, its construction, and advantages over other 

 types of furnaces, and the manner of charging it, together 

 with the appliances necessary to a foundry in the shape 

 of drying stoves, laddies, cranes, etc., and a " fettling 

 shop " for the ultimate cleaning and dressing of castings 

 were duly considered. 



The author then treated of the examination of cast-iron 

 work and the care that should be observed in all inspec- 

 tion of the same, and finally discussed the tests usually 

 applied and the general strength of cast-iron. 



LEEDS GEOLOGICAL ASSOCIATION. 

 At the meeting on Oct. 25th, Mr. J. E. Bedford, F.G.S., 

 the President, delivered an address on "The Oil Fields 

 of the United States and Russia." There are now, he 

 said, two large centres from which petroleum products 

 are derived — the State of Pennsylvania, in the United 

 States of America, and the district of Baku, in Southern 

 Russia. To the Americans is due the credit of having 

 developed an enormous trade and of benefiting the world 

 at large. Paraffin is the most generally known product 

 of the petroleum industry. It is obtained by distillation 

 of the crude petroleum in large retorts or stills. When 

 the heat rises to the boiling point the distillation com- 

 mences, and the lighter spirit or gasoline, generally 

 called benzoline, is the first product. When this is all 



