ISS?.*] THE DIATOMACE^. 125 



The specimens thus collected are to be examined at home. 

 Portions of each may be preserved either in the mass^ or by di- 

 luting a little mth a few drops of "water, spreading it on a slip of 

 glass, and e^^'aporatiug to dryness. These slips are wrapped in 

 paper, on which the necessary notice is to be written, and ar- 

 ranged systematically or alphabetically, no matter, so that each 

 object can be readily found when wanted. Diatoms are some- 

 times preserved in spirit, on account of the organic contents re- 

 maining, in this medium, almost unchanged. 



For the investigation of the Diatomacea a microscope magni- 

 fying from 250 to 300 diameters is necessary.^ Besides the mi- 

 croscope, a good lens, forceps, glass rods, needles and handle, 

 together with some hair-pencils for cleaning the eyeglass, are 

 necessary. Suitable glass slides, and thin glass for covering the 

 object, are sold by the optician : care should be taken that the 

 surface of both glasses be perfectly even. 



Thus equipped, we commence om' investigations. A portion, 

 the size of a pin's head, is taken from the specimen to be ex- 

 amined, laid upon a slip of glass, diluted with a drop of watei", 

 covered with a piece of thin glass, and placed under the micro- 

 scope. The whole surface of the covering-glass must be in con- 

 tact, any obstacle being easily removed by the needle, and air- 

 bubbles must be guarded against. For the better recognition of 

 the object, specimens may be exposed to a red-heat, and after- 

 wards examined. t This renders their structure and specific cha- 

 racters more evident, and admits of their accm'ate delineation, — 

 a process requiring particular apparatus and considerable skill, 

 but which possesses many recommendations. 



Warwick, April, 1857. 



* Eabeiihorst mentions several microscopes of this description by foreign makei*s. 

 I am credibly iixformed that Sir. Baker, EiS and 244, High Holborn, manufactures 

 an iustriunent, price two guineas, which answers every piu'pose. It is capable of 

 magnifying 300 diameters. — H. J. C. 



t lustead of employing a red-heat, specimens may be advantageously placed in a 

 test-tube, aud boiled in strong nitric acid over the spu-it-lamp or gas. The acid 

 must be poured off after the sediment has quite subsided, and this sediment washed 

 several times in water, to guard against the deposition of crystals of nitrates on the 

 glass slides. The damp sediment is placed on a sHp of glass, a di'op or two of 

 water added if necessary, t hin ly spread over the glass, and the moistm-e evaporated. 

 Each specimen should be carefully examined prior to the acid-treatment.— H. J. C. 



