xxiv INTRODUCTION. 



the object as required. If a very minute quantity be desii-ed, the lower part of the stopper 

 is allowed to touch the inside of the neck of the bottle when it is withdrawn, and if a larger 

 quantity be required this proceeding may be avoided. Each bottle should be labelled, and 

 a label should also be placed upon the upper end of the side or partition of the box neai' to 

 the bottle, so that the nature of the contents of each bottle may be ascertained without re- 

 moving it from the box. The general advantages of this apparatus are, that the quantity 

 of reagent required can be obtained to the greatest nicety, and it can be added to the exact 

 spot required with one hand only, so that the other can be employed to hold the slide and 

 object, &c. Mr. Ferguson, of Giltspur Street, supplies these at a small cost, after our 

 pattern. 



Reagents or test liquids. — Some of these should be kept in the test-bottles ; but larger 

 quantities should also be kept in other stoppered bottles. We give a hst here of those test 

 reagents which are most frequently required ; the method of preparing each, the strength, 

 &c., will be found under the respective heads. 



1 Sulphuric acid. 2. Nitric acid. 3. Acetic acid. 4. Caustic potash. 5. Chloride of 

 calcium. 6. Aqueous solution of iodine. 7- Oil of turpentine. 8. Syrup. 9. Acid 

 nitrate of mercury (Millon's test liquid). 10. Distilled water. 



^ther and alcohol should also be kept at hand. Chromic acid should be preserved in a 

 wide-mouthed stoppered bottle, and its solution prepared when requisite, as it easily be- 

 comes decomposed by dust, &c. 



Troughs — are flat, oblong, glass boxes, without lids. They are made of pieces of glass 

 cemented together by marine glue, and are used in examining the larger aquatic plants or 

 animals in a living state ; also in mounting objects. 



Divided Scale. — A metallic or ivory scale divided into lOOdths, &c. of an inch, is indis- 

 pensable in micrometric admeasurements (see Measurement). The metal or ivory should 

 extend beyond the graduated portion. 



Micrometer. — A glass slide with fine lines scratched upon it with a diamond, these being 

 ToVo^^^ of an inch apart, is absolutely requisite. Another, with coarser divisions, is also 

 required to be placed in the eyepiece, for making measurements (see Measurement). 



A piece of tin plate, or sheet iron, 5 or 6 inches square, is requisite. This is supported 

 upon one of the rings of a retort stand, a tripod, or some equivalent, and heated by a spirit- 

 lamp placed beneath. It is of use in macerating objects upon shdes in chemical reagents, 

 oil of tm'pentine, or Canada balsam. An elegant substitute is found in the brass table 

 made by Messrs. Smith and Beck. 



Ring-Net. — A very useful piece of apparatus for collecting Desmidiaceae, Diatomacese, &c., 

 where entangled amongst Confervse, &c., or forming crusts or films upon other aquatic 

 plants, consists of a wooden ring about 4 inches in diameter, furnished with a groove all 

 round its circumference, in which also a radial aperture exists, through which the end of a 

 stick may pass. A piece of very fine muslin, rather larger than the ring, is then laid over 

 it, and the margins of the muslin fixed in the groove by means of a vulcanized Indian-rubber 

 ring. Thus we have a kind of strainer, and by using several pieces of previously wetted 

 muslin in succession, a large number of the minute organisms may be separated from the 

 water. The pieces of muslin may be brought home, folded up, in wide-mouthed bottles, 

 separately, or several in one, according as the organisms are obtained from one or several 

 waters. In this way we save carrying a large quantity of water. The pieces of muslin are 

 afterwards opened and placed in jars of filtered river-water, and exposed to the light, when 

 the organisms will become detached. 



A single microscope, or some apparatus which will allow of dissection with the aid of 

 lenses, is essential, provided an erecting eyepiece, or the erector of Messrs. Smith and Beck 



