REAGENTS 41 



tiire indicated on the labels is reached. The fact that the price rises 

 with the melting-point may explain the discrepancy. Test every grade 

 with a thermometer. If it is desired to get a paraffin melting at 52° C. 

 and your sample melts at 50° C, add a little paraffin with a melting- 

 point above 52° C. ; if the sample melts at 55° C, add a httle with a 

 melting-point below 52° C. 



Grubler's paraffins need no modification, but paraffins only slightly 

 inferior can be improved by the addition of bayberry wax. A piece of 

 the wax, not larger than a grain of com, to a pound of paraffin, is hke- 

 ly to improve the infiltration and cutting. 



Paraffin may be used repeatedly. Keeping it in the Hquid condi- 

 tion in the bath month after month has an advantage, since it be- 

 comes more and more tenacious and homogeneous. 



Glycerin, glycerin jelly, Venetian turpentine, and gold size are de- 

 scribed in the chapter on "The Glycerin Method" (chap. vii). Cel- 

 loidin is described in the chapter on "The Celloidin Method" (chap, 

 x), and cellulose acetate in the chapter on "The Cellulose Acetate 

 Method" (chap. xi). The reagents already described are noted further 

 in connection with specific applications. Reagents used in making mi- 

 crochemical tests are described in the chapter on "Temporary Mounts 

 and Microchemical Tests" (chap. v). 



A list of reagents will be found in chapter xxxi. 



Cleaning fluid. — No matter how nice they may look and no matter 

 what dealers may claim, slides and covers, as you buy them, are never 

 clean. This is a good cleaning fluid: 



Potassium dichromate 2 g. 



Water 10 c.c. 



Sulphuric acid 23 cc. 



Dissolve the potassium dichromate in water and add the sulphuric 

 acid. 



For cleaning slides and covers, this solution may be diluted 25 or 

 even 50 times with water. 



Leave slides and covers in the solution for 24 hours, rinse thorough- 

 ly in water, and then put them into soapy water and leave them over- 

 night or 24 hours. Rinse thoroughly and wipe dry. If the least trace 

 of acid is left, many stains will fade. 



For developing trays and most kinds of laboratory glassware, the 

 solution can be used, full strength, for a few minutes or an hour. 



The solution can be used repeatedly. 



