V. - HYDROMETERS. 145 



664a. Apparatus by Rakowitsch for testing Alcohols and 

 Saccharine Matter in Liqueurs ; likewise for ascertaining the 

 fatness of butter, and for testing water. 



R. Nippe, St. Petersburg. 



665. Apparatus for determining the Specific Gravity 



of bodies, inclusive of a thermometer. 



Ch. F. Geissler $ Son, Berlin. 



670. Parabolic Diagram of the relation between tension 

 and volume of the saturated steam. 



H. Hddicke, Demmin, Pomerania. 



This parabolic tension diagram shows that it is justifiable to replace 

 Mariotte's oder Pambour-Navier's tension-lines of the saturated steam by a 

 parabola. This method gives for the ratio of the mean pressure (p ) on one 

 side of the piston to the absolute pressure at the commencement (p), and 

 the cut off (e) the elementary formula: p =p % (10 2 (4 p+1) 2 , or 



4p+l ' 



(See " Practical Tables and Rules for Steam Engines," by H. Haedicke 

 Kiel, 1871.) 



671. Piknometer. Dr. H. Geissler -, Bonn. 



672. Two Sets of Areometers. Dr. H. Geissler, Bonn. 



673. Manometer for Minute Observations, used by A. de 

 la Rive in all his latest researches concerning the propagation of 

 electricity in rarefied gases. 



De la Rive Collection, the property of Messrs. Soret, 



Perrot, and Sarasin, Geneva. 



This instrument, constructed by the Geneva Association for the Construc- 

 tion of Scientific Instruments, consists of two glass tubes dipped in a common 

 mercury trough, of which one is a simple locomotive tube serving as a point 

 of comparison, the other communicating on its top with the quantity of rarefied 

 gas by means of a pipe adjusted in the setting of the apparatus. The pressure, 

 that is, the difference between the two mercury columns, is read by means of 

 a small cathetometer, of which the millimetric graduation is turned towards 

 the tubes and the lamp which lights them both. This graduation is reflected 

 in the telescope by means of a full reflecting prism placed before the objective. 

 Thus the level is at once read, and a micrometrical division placed at the focus 

 of the eye-piece shows the ^ of the millimetre. 



673a. Delicate Pressure Gauge. 



Dr. K. List, Hagen, Westphalia. 



The very light pressure required to produce a current through the stoA es 

 can be shown by the delicate pressure gauge (enclosed in a mahogany case), 

 which has a thin diaphragm exactly one square foot in area, and has a light 

 lever and weights to cause it to bear the pressure brought on its surface, 

 so that the whole pressure of the air on one square foot is exactly weighed 

 with ease. As small a pressure as one hundredth of an inch of water can be 

 measured. 



39508. K 



