222 ELEMENTAKY PHYSIOLOGY. [XXL 



40 C.,) squeezing the pieces; filter through a 

 coarse filter. A crude solution of haemoglobin 

 is thus obtained. 



4. Arrange a spectroscope so that the spectrum of 

 a flame and the scale are distinctly seen 1 . Hold 

 in the flame a wire having a few crystals of 

 common salt upon it and observe the bright 

 yellow sodium line (D). Shift the scale so that 

 the sodium line is at 5 8' 9 of the scale and 

 clamp the spectroscope tubes. 

 The numbers on the scale indicate wave-lengths 

 in hundred-thousandths of a millimetre, so that 

 each division corresponds to a difference of a 

 hundred thousandth of a millimetre, and each 

 tenth of a division corresponds to a millionth of 

 a millimetre, in wave-length. The wave-length 

 of the line D is 589 millionths of a millimetre, so 

 that when this line is placed at 5S'9 of the 

 scale, the wave-lengths of the parts of the 

 spectrum can be read off on the scale 8 . 

 The spectra described below should be carefully 

 drawn on a blank scale like that of the spectro- 

 scope, the position of Frauenhofer's lines B, C, D, 

 E, F being filled in from the following table 



1 Cp. Gamgee, Physiol. Chemistry i. 93. The Demonstrator \vill 

 shew the method of using the instrument. 



2 If this scale is not present in the spectroscope used, the position 

 of the sodium should be observed; bring then the micrometer wire 

 exactly over it and read off cu the vernier the position of the telescope. 

 In the subsequent observations when the telescope is brought into the 

 position read off, the micrometer wire will give the position of the D 

 line. 



