438 Dr. E. J. Mills on the Detached Colorimeter, 



still been left for an apparatus from which leakage at the bot- 

 tom is impossible, and in which, as in the common detached 

 colorimeter, the liquid comes into contact only with glass. 



The new detached colorimeter* is 

 made in two pieces, alike in every re- 

 spect ; one of these is represented in the 

 subjoined figure: — It consists of a stout 

 glass tube having a broad flat foot, and 

 graduated into 100 equal parts ; its 

 capacity at the upper part is about 120 

 cubic centims. On the top of this is a 

 loosely fitting brass cap, prolonged down- 

 wards so as to cover and shade the sur- 

 face of the liquid, thereby preventing the 

 appearance of a dark meniscus. The 

 surface of the liquid is only visible side- 

 ways through the little aperture a, cut 

 out for that purpose. The cap is perfo- 

 rated centrally; and a short tube t rises 

 from the perforation. This tube is sol- 

 dered laterally to a narrower one t f . and 

 this again to a small block b } from which 

 rises a spring carrying another small 

 block b' . The tube t' has, cemented into 

 it, a glass tube u, which passes straight 

 downwards, and reappears below the flat 

 surface of the cap, its end amply clear- 

 ing that surface. This tube is coned 

 outwards at its upper extremity, but is 

 left plain below. Through it there passes, 

 with just sufficient room to move, the 

 rod r r, bent below twice at right angles, 

 so as to carry a flat circular " opal " glass disk, to which it is 

 attached by fusion. These disks are turned in the lathe: their 

 surfaces should be polished free from scratches, and their edges 

 show no bevel. The rod is prevented from falling by the easy 

 pressure of the little half-tube h, carried by the block V . When 

 the thumb and fore finger are lightly pressed on x and a/, the 

 rod can be readily moved up and down, and will then stay in 

 any position in which it may have been left. It is convenient , 

 to cone outwards the half-tube h at both its ends ; but only 

 traces of liquid ever reach this spot. 



The instrument has two accessories which are of consider- 

 able service. These consist (1) of a pair of glass disks, d, 



* The instrument has been made for me by Messrs. Cetti and Co., 

 Brooke Street, Holborn. 



