328 ACCESSORY APPARATUS 



The Method of using the Micro-spectroscope, The objects to be 

 investigated are of two sorts, liquid and solid. Colouring substances, 

 as chlorophyll, the colouring matter of hair, blood, &c., will fre- 

 quently come under inicro-spectroscopic investigation in the form of 

 a solution. In general we need scarcely say anything concerning 

 the preparation of the solution. In reference to the chlorophyll of 

 the phanerogams especially, the particular part of the plant from 

 which the preparation is to be made, as, for instance, the foliage 

 leaves, is put for a short time in boiling water, then quickly dried 

 by means of bibulous paper, and then immersed for a longer time in 

 absolute alcohol, ether, or benzole in a dark place, for the purpose 

 of extracting the chlorophyll colouring matter. The concentration 

 of the solution thus produced, which influences the intensity of the 

 absorption spectrum and the number and length of the absorption 

 bands, depends naturally upon the time during which the material is 

 in the extracting medium, as well as on the quantity of the material. 



Commonly also a solution of less concentration will give the same 

 intensity of spectrum if a sufficiently thick layer of it be used. The 

 solution can generally be examined in an ordinary test-tube. The 

 test-tube is filled and carefully corked, and then laid on the stage of 

 the microscope or held before the opening of the comparison prism, 

 as the case may be. For the latter purpose (bringing liquids before 



the opening of the comparison prism) a small open trough of glass, 

 with two parallel glass plates, is very useful. For exact investiga- 

 tions, however, the trough-flask is preferable. It is a flask whose 

 two sides, back and front, are parallel, furnished with a carefully 

 fitted ground-glass stopper. It should be filled quite full of the 

 solution and then laid with its broad side on the stage. It is 

 especially indispensable when we wish to study the combination 

 spectrum of two solutions. In that case two flasks are filled each 

 with a different solution, and both laid upon the stage, one upon 

 the other. For the purpose of examining small quantities of 

 any liquid, a sufficient depth being obtained with very little 

 material, vertical glass tubes attached to horizontal plates are used, 

 as proposed by Mr. Sorby and shown in fig. 276. The narrow tubes 

 are made of various lengths from sections of barometer tubing, in 

 order to present different thicknesses of the contained fluid, the 

 broad tube being higher on one side than the other, and thus con- 

 stituting a wedge-shaped cell, which, when filled and closed by a 

 thin cover-glass, will present a varying thickness of fluid for study 

 and comparison. If the object to be investigated is not a solution, 

 but a preparation of the kind which we commonly employ in micro- 

 scopic inquiries, we must first of all bring it into the focus of the 

 objective system. To do this we must first remove the tube bearing 



