344 



SCIENTIFIC NE^A^S. 



[April 13, 18 



Detection of the Presence of Organic Matter in 

 Drinking Water. — This process depends on the 

 reduction of salts of silver in contact with organic matter 

 on exposure to the light of the sun. We put, says 

 Cosmos, into a stoppered bottle of clear white glass, and 

 capable of containing one pint, half a pint of the water in 

 question. To it are then added 100 grain measures of a 

 neutral solution of nitrate of silver, containing five per 

 cent, of the solid salt. The bottle is stoppered and set 

 in the sun until all the silver is reduced, which may take 

 from twelve hours to five days. When the water 

 becomes clear, it is filtered, and washed first with 

 distilled water and then with ammonia. If anything 

 remains undissolved, organic matter is present in the 

 virater. 



A New Sugar Cane. — For about 100 years most of 

 the sugar in the West India Islands has been obtained 

 from the Otaheite cane, originally brought from the 

 Pacific Islands by Captain Bligh in His Majesty's 

 ships in 1796. Latterly strenuous efforts have been 

 made to introduce new canes in the hope that 

 they would prove richer in yield of sugar. In one in- 

 stance we learn that a cane introduced by the present 

 Assistant-Director of Kew Gardens when in charge of 

 the Botanical Gardens at Jamaica has supplanted the 

 Otaheite cane and proved most productive. A planter 

 at St. Kitts says the new cane, which he has called the 

 Jamaican, is a " marvellous cane." He adds that " it 

 stands dry weather well, and is entirely superseding the 

 Otaheite cane." — Times. 



Experiments on Milk and Butter. — At the New 

 York Dairy and Cattle Show in May last, it appears 

 that the prizes for largest quantity of milk and of butter 

 produced were awarded to Holstein cows in opposition 

 to Jersey cows. It appears, however, that whilst on an 

 average 30' 5 2 lbs. of the milk of Holstein cows was 

 required to yield i lb. of butter, only 20' 11 lbs. of that of 

 the Jersey cows produced the same quantity. Hence the 

 milk of the Jerseys is richer by one part in three. No 

 analysis of the milk was made. On analysing the 

 butters, the mean proportion of water in the Holsteins 

 was found to be 18 'go, whilst that in the Jerseys was 

 only 1 6-63 per cent. The proportion of milk and butter 

 yielded to the total weightof each cow and to the quantity 

 of food consumed is not stated — two very important 

 items. 



The Action of Manures. — M. Berthelot concludes 

 (Comp/es Rendus) that the addition to the soil of 

 phosphatic manures, and to a certain extent even that of 

 nitrogenous fertilisers, after the normal time of flowering 

 of the crop seem useless, or, at least, of small value, 

 whilst the addition of potassic manures may render 

 service nearly up to the end of the season of vegetation, 

 seeing that potash continues to be absorbed and to act as 

 long as the formation of woody matter is in progress, 

 even during the period of fructification. He adds that 

 phosphatic manures act upon the vegetation of the 

 season only by that portion which is immediately 

 soluble, and which is assimilable before flowering. The 

 effects of the portions which are only gradually attacked 

 by earthy and terrestrial agents seem to be postponed for 

 the crops of succeeding seasons, 



Carbons for Arc Lamps. — The manufacture of arc 

 light carbons forms an industry of considerable magni- 

 tude, and the works of Herr Hardtmuth, in Dfibling, are 

 now turning out about 3,500 metres of carbons daily. 

 Some improvements have recently been made in the 

 process of manufacture, by which the homogeneity 

 and density of the carbons are increased. These refer 

 more especially to cored carbons. As usual, the rod of 

 plastic material issues from the press in the form of a 

 tube, and after drying and baking the carbons are 

 steeped in a heavy hydrocarbon, by which the pores left 

 after the first baking are filled. The carbons are again 

 baked, and the core is then inserted under a pressure not 

 much greater than that of the weight of the plastic mass 

 forming the core. In connection with this factory is a 

 well equipped electrical laboratory for the testing of arc 

 lamps. There are dynamo machines by various makers, 

 viz., Poge, of Chemnitz ; Kremenezky, Mayer, and Co., 

 of Vienna; Krizik, of Prague; and Siemens and Halske 

 (alternator). The reason for installing various dynamos 

 is to be able to test any lamp which may be sent to the 

 laboratory. There is also a spectroscope for determining 

 the elements contained in the carbon from the spectrum 

 of the arc, and the laboratory is equipped with the usual 

 electrical measuring instruments and photometers. The 

 work at this laboratory is done on a thoroughly scientific 

 basis, and both lamps and carbons are tested so as to 

 determine the best quality of carbon to be used for each 

 type of lamp. At the forthcoming Jubilee Exhibition 

 Hardtmuth carbons will be largely used for the arc lamps. 

 — Industries. 



Insulating Cement. — According to the Moniteur In- 

 dustriel, the Director of the Vesuvius Observatory pos- 

 sesses an electrometer which is supposed to be the most 

 perfect instrument of its kind. It was in reference to 

 this instrument that M. Mascart observed, at the Meteo- 

 rological Congress held in Rome — "So perfect is it that 

 it might serve to control the indications of all other in- 

 struments of the same class in the world." This 

 superiority is said to be due to the material with which 

 the insulation is effected, viz., a cement formed of pitch 

 from Greece [poix grecqiie), two parts ; and calcined 

 plaster, one part. The plaster in question, termed in 

 Italian scagliola, is pure gypsum, which has been raised 

 to a high tempefature and thus deprived of half its water 

 of constitution. It is a superior kind of plaster of Paris, 

 and, when mixed with water, hardens after combining 

 with the proportion of this fluid which had been expelled 

 by heat. The cement formed by admixture of the pitch 

 with this plaster (presumably in the semi-dehydrated 

 condition) is, when hot, a homogeneous viscid paste ; it 

 may be applied lo apparatus by means of a brush, or it 

 may be cast in moulds of any required form. It pos- 

 sesses the insulating properties of ebonite, but is softer 

 and more plastic. A skilful manipulator can turn and 

 polish it in the lathe. In colour it is s'ightly darker 

 than amber. From the electrical point of view, its 

 characteristic and useful property is that it retains its 

 insulating power, whether it be exposed to a high tem- 

 perature or a moist atmosphere. We may add to the 

 above that, at the period when Peltier's or Milner's 

 electrometer was in common use for testing the insulation 

 of cables, we obtained the most perfect insulation with 

 a cement composed of shellac, gum dammar, and paraffin 

 wax. 



