112 MICEOSCOI'ES FOR 



tilled water, but tLe tlikd is fatal to its employment in a pui'e state, 

 hence various formulae have been proposed, of which the following 

 are the chief : — 1. Biine, that is, a solution of common salt in water. 

 2. Alum dissolved in water. 3. Corrosive subhmate (bichloratc of 

 merciu-y) in water. 4. Sulphate of the peroxide of hon dissolved in 

 water. 5. Sulphate of zinc dissolved in water. 6. Sal ammoniac 

 (hydi'ochlorate of ammonia) in water. One or other of these solu- 

 tions are recommended by different naturaHsts, while those who 

 recommend the same, differ, in the degi-ee of concentration necessary. 

 In all cases it is advisable to use distilled water, and to filter the 

 solution tlu'ough bibious paper. 



Aqueous compound solutions are also employed, but these vaiy 

 greatly. 1 . Dr. Goadby used the following as a preserving fluid, 

 and has had great experience : bay salt 4 oz. ; alimi 2 oz. ; corrosive 

 sublimate 4 grains ; and boiling water 2 quarts. These are to be well 

 mixed and filtered. 2. Bay salt 3| lbs. ; con-osive sublimate 7 grains ; 

 and water 6 quarts. 3. Arseuious acid 2 di'achms; bay salt 3 lbs. ; 

 and water 6 quarts. 4. Another fluid is composed of alum 3 parts ; 

 common salt 1 part, and water 24 parts. 



Alcohol, creosote, chromic acid, sugar, and glycerine, have each 

 been employed as preserving fluids. The fii'st two require large 

 additions of water to prevent them from corrugating the specimens. 

 Thus five parts of water is used with one of alcohol. Mr. Thwaite"s 

 fluid, which is very excellent, is composed as folloAvs : distdled water 

 16 parts, rectified spuits of mne 1 part, saturated with a few drops 

 of creosote. To this mixtiu-e he adds a little prepared chalk, filters, 

 end adds an equal mcasm'e of camphor water. 



In some cases Canada balsam mixed Avith castor oil has been used, 

 while gum water, when slowly diied with the specimens, and after- 

 wards surroimded by a varnish, often answers very well. 



The mechanical contrivances for secui-iug the specimens and fluid, 

 are as various as the fluids. 



The size of the glass shdcs should be miiform, the usual length 

 generally adopted, is that given ia my little work entitled a List of 

 2000 Microscopic Objects, namely, tluee inches : the width will vtuy 

 to suit the prepaiations, but one inch is that most usual. Having 



