QUANTITATIVE MICROSCOPIC DETERMINATIONS 



157 



in a container is not satisfactory. If the amount of the material is 

 considerable, (20 grams and more), divide the thoroughly mixed ma- 

 terial (spread out in a circular layer) into quadrants, remove one quad- 

 rant and again mix this thoroughly by means of a suitable spatula. 

 A second division may be made if necessary. The final sample should 

 be not less than 5 grams. 



4. Making the Diluted Suspension. Dry the thoroughly mixed 

 sample for one hour at a temperature of 80C. Weigh out 5 grams 



a 



FIG. 35. Special counting chamber for making quantitative microanalyses of 

 foods, spices and drugs. The two glass slips upon the extra size slide are ex- 

 actly 0.2 mm. thick and the area bounded on two sides by the two slips is 10 

 sq. cm. (1,000 sq. mm.). 0.2 cc. suspensions of this material to be examined is 

 spread in this area and covered with the rectangular cover glass (6). Full size. 

 (Made by the Bausch and Lomb Optical Company.) 



of the sample and place it in a 25 cc. graduated cylinder, add 10 cc. of 

 distilled water (or 10 cc. of a mixture of equal parts of distilled water 

 and glycerin) and mix thoroughly by means of a glass rod. Fill up to 

 the 25 cc. mark with a 5 per cent, gum acacia solution and again 

 thoroughly mix. The gum solution will hold the tissues in suspension 

 until the microscopic examination is made. The above makes a 

 dilution of 1-5, which will be found satisfactory in most cases. 

 Higher dilutions, as 1-10, 1-25, 1-100, may be used if desired or if 

 necessary for accurate results, as in starch counting. 



Other suspending media may be used, as glycerin, oils, a thin syrup, 



