Nut fair* Mctlxxl 



317 



The accompanying figure shows a little apparatus which I have 

 made in the laboratory, and have found very convenient for making these 

 measurements of the amount of precipitum. A fairly large thermometer 

 tube (A) is used, which is graduated in tenths of a c.c., the calibre 

 being chosen so that a fine steel scale of 10 cm. (E) subdivided into 

 0'5 mm. corresponds to the length of column of fluid measuring O'l cm. 

 in the tube. The tube is filled with pure water up to the graduation 

 mark (not shown in the figure), the mouth being wiped dry with filter- 

 paper. The tube is fixed in a spring clip which is attached to the 

 wooden rod (D) so that it pivots in a vertical plane, thus permitting the 

 tube to rest in a horizontal position or at any desired angle. The rod 

 (D) slides horizontally between the rods C and C', which are nailed to 

 a solid block of wood beneath. Two small brass plates attached to 

 rod C prevent rod D from being displaced. The steel cm. measure is 

 attached to a metal support, which is screwed to the block beneath. 

 By a lucky chance I happened to have an old " peep-sight " from a 

 sporting rifle which served admirably for carrying the metal scale, as 

 it can be inclined at any angle and be screwed up or down. By 

 pivotting the scale on a screw passing through the eyehole of the sight, 

 the scale can be placed and retained at any angle on its support, thus 

 making it possible to closely apply the fine scale to the thermometer 

 tube in any position desired. 



Fig. 5. 



The height of the volume of precipitum having been marked upon 

 the capillary tube, the latter is cut square by means of a diamond at the 

 lower meniscus, a small quantity of air having been left in the lower end 

 of the tube when it was sealed. Tin- contents ,,f the tube aro blown out, 



