516 Scientific Intelligence. 



15-6° C./15-6 C. Table II shows the indications of Sikes' 

 hydrometer and the percentages of British proof spirit, American 

 proof spirit, of ethyl alcohol by weight, and also by volume at 

 15° C. and 15 - 6° C. Table III compares the indications of Sikes' 

 hydrometer with those of Russia, Holland, Spain, and Switzer- 

 land. H. L. W. 



V. Brief Course in Metallurgical Analysis ; by Henry 

 Ziegel. Large 8vo, pp. 72. Easton, Pa., 1915 (The Chemical 

 Publishing Co.). — This small book has about one-half of its pages 

 left blank for notes. A fairly extensive and well-selected list of 

 analyses is outlined, and references are made to the best works on 

 the subject. It appears, however, that the directions given are 

 often not full enough for a student's use, that the language is 

 frequently ambiguous, and that some of the advice given is not 

 the best. h. l. w. 



8. Characteristics of Long Direct- Current Arcs. — In an 

 earlier paper (see this Journal, vol. xxxviii, p. 362, 1914), W. 

 Grotrian used a direct-current dynamo capable of generating 3 

 amperes at 5000 volts in demonstrating experimentally that the 

 so-called cyanogen bands owe their origin to nitrogen alone and 

 not to the presence of carbon in the arc. In a more recent paper 

 he has recorded the following interesting results obtained with 

 essentially the same assemblage of apparatus. 



The electrical characteristics of arcs, whose lengths were varied 

 from a few millimeters to 50 centimeters, were obtained with 

 carbon, copper, and iron electrodes in air, nitrogen, oxygen, car- 

 bon dioxide, hydrogen, and water vapor. It was found that the 

 gas was chiefly responsible for the course of the characteristics 

 while the material of the electrodes had only a very slight 

 influence on the curves. 



In all cases where the axis of the arc consisted in a well- 

 defined luminous band the Ayrton formula 



Vi = a + fil + yi + 8li 



reproduced the experimental data very satisfactorily. [ T" 

 voltage across arc, i = current, and I = length of arc] The 

 following numerical results were deduced 



Vi— 32-6^ + 622 + ll'4tli 



nitrogen 



carbon dioxide Vi = —90 + 131 + 80i + 1V1U 



hydrogen Vi = 180 + 222/ + 290li 



water vapor Vi = lS5l + 200i + lOli 



As would be expected, the temperature of the core of the arcs 

 was so high that platinum and other metals liquefied in it at 

 once. On the contrary, the little rods of Nernst glowers with- 

 stood the high temperature without undergoing appreciable 

 modification and hence they could be used as the terminals of 

 exploring circuits, that is, as electrical sounds. In the air-arc it 



