BLOOD ANALYSIS 



293 



is kept constant. The box is conveniently 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 nephelometer and the light source may be 

 seen in the diagram, Fig. 84. The lamp used is an ordinary 50- 

 watt tungsten ("Mazda") supported 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 



FIG. 85. LENZMANN-KOBER NEPHELOMETER. 



minutes, since it consists essentially only in unscrewing the brass 

 plate carrying the plungers 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- 

 ter where the cups move and the prisms are stationary. The changes 

 required to convert the older type of instrument are more complicated 

 and scarcely to be advised unless the instrument is to have fairly 



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

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



