BLOOD ANALYSIS 



297 



The openings in the prism case, particularly the lower ones, should 

 be protected against accidental splashing by thin glass plates (thick 

 cover slips) which are held in place by a little glue. 



Artificial light is necessary and the lamp should be enclosed in 

 a tight box into one end of which the nephelometer fits snugly. A 

 partition extending part way up the box as shown in the diagram 

 (Fig. 95) serves the double purpose of shutting off the light from 

 the lower part of the instrument 

 and of providing a stop against 

 which the instrument is pushed, 

 so that its distance from the light 

 is kept constant. The box is con- 

 veniently made without a bottom 

 and the end closed with a dark 

 curtain after the nephelometer is 

 pushed into place. The inside of 

 the box should be painted black. 

 A dark room is desirable but not 

 necessary, as the instrument may 

 be used satisfactorily in a room 

 darkened by a dark shade or even 

 in a dark corner of the laboratory. 



The relations of the nephelo- 

 meter and the light source may 

 be seen in the diagram, Fig. 95. 

 The lamp used is an ordinary 50- 

 watt tungsten ("Mazda") sup- 

 ported by a bracket about 30 cm. 

 from the nephelometer and at the 

 height of the nephelometer tubes. 

 The change from one instrument 

 to the other can be made in one 

 or two minutes, since it consists 

 essentially only in unscrewing 

 the brass plate carrying the plun- 

 gers and screwing on the plate to carry the nephelometer tubes. The 

 extra parts needed, plate, tubes, and jackets, are few and can be made 

 if necessary from material at hand in any laboratory and by anyone 

 with a slight degree of mechanical skill. 1 



The above description applies only to the later type of colorime- 



1 The extra parts necessary for the conversion of the colorimeter into the nephelometec 

 may be obtained from the International Instrument Co. of Cambridge, Mass. 



FIG. 96. KOBER'S NEPHELOMETER 



COLORIMETER. 



(From Journal of Biological Chemistry, 

 29, 155, 1917.) 



