WITH THE MICROSCOPE. 55 



Dr. Maddox tells me that for some years past he has been in the habit 

 of using equal parts of sweet spirits of nitre (Sp. Eth. Nit. of the Phar- 

 macopoeia) and glycerine, especially in preparing delicate tissues of 

 insects. He finds that many objects are rendered very transparent 

 if washed in this medium, before they are preserved in glycerine. 



Glycerine used to be obtained by boiling oil with litharge. The 

 oleitte of lead remains as an insoluble plaster, while the glycerine is 

 dissolved. It may be rendered free from lead by passing a current 

 of sulphuretted hydrogen through it ; and the clear solution, after 

 filtration, may then be evaporated to the consistence of a syrup. 



The glycerine which is now distilled by a patent process, and 

 known as Price's glycerine, is much superior to the ordinary glycerine. 

 It is perfectly colourless, free from all impurities, and of much greater 

 density. The specific gravity of Price's patent glycerine is 1240, 

 while the common is only 1196 '6. The former costs about 4*. and 

 the latter is. 6d. a pound. 



For more than fifteen years I have used glycerine for preserving 

 almost every structure. I shall give the results of my most recent 

 experience of this substance, from the use of which I have learnt 

 more than from any other preservative medium, in part V, where 

 also the advantages of glycerine are discussed. 



101. Tlnvaites' Fluid. This fluid has been much employed by 

 Mr. Thwaites for preserving recent specimens of desmidiae ; but it 

 is also applicable to the preservation of a vast number of animal 

 substances. 



It is made as follows : 



Water . . . 16 ounces. 



Spirits of wine ... i ounce. 



Creosote, sufficient to saturate the spirit. 

 Chalk, as much as may be necessary. 



Mix the creosote and spirit, stir in the chalk with the aid of a 

 pestle and mortar, and let the water be added gradually. Next add 

 an equal quantity of water saturated with camphor. Allow the 

 mixture to stand for a few days and filter. In attempting to 

 preserve large preparations in this fluid, I found that it always became 

 turbid, and therefore was led to try several modifications of it. 

 The solution next to be described was found to answer very satis- 

 factorily. 



Water may also he impregnated with creosote by distillation. It 

 should be remarked that M. Strausdurkheim has succeeded in pre- 

 serving animal preparations in camphor water only. 



