PRESERVATION OF SPECIMENS IN PLASTICS 5 



In like manner type SB-1055 fluid can be prepared by making a 

 nixture that consists of 50 percent each of SB-1035 and SB-1075, and 



ype SB-1065 fluid can be made by using 25 percent of SB-1035 and 

 75 percent of SB-1075. 



A full series of the nonreducing fluids with values in 1.0 or preferably 

 0.5 steps, from pH 3.5 to pH 7.5, is desirable, because these fluids are 

 ased for preserving material containing anthocyanin pigments that 



equire close correspondence between their specific pH values and 

 those of the fluids with which they are treated. In the case of the 

 reducing fluids, however, intermediate pH values are not ordinarily 



eeded, because the stock fluids of this type are designed to meet the 



H requirements of the principal pigments for which they are intended. 

 All regular fluids can be converted to the A form by the addition of 



.1 percent of the surface-active conditioning mixture consisting of equal 



arts of Santicizer B-16 and Tween-20. This A form, e.g., SB-1035-A, 

 s preferable for most specimens, except where dense pubescence is 



resent, because it is more rapid and uniform in its action. 



Measurement of Preserving Fluid pH Values 



Because of their high solids concentrations the pH values of the 

 preserving fluids can be measured more satisfactorily with a colorimetric 

 comparator than with an electrometric instrument. Comparators of 

 [the LaMotte type or of the Taylor or Hellige types are particularly 

 suitable for making these measurements, although pH test papers may 

 be found to be accurate enough in many instances. The hydrogen-ion 

 concentration tends to vary with changes in the amount of water in 

 these fluids, and it is, therefore, advisable when making pH measure- 

 ments to add sufficient distilled water to the sample of fluid in the 

 comparator test tube to bring it to a uniform solids concentration of 50 

 percent. Since the solids content of most of the preserving fluids 

 mentioned in this publication is approximately 80 percent, the amount 

 of water needed to bring it down to 50 percent would be 60 percent of 

 the original total weight. 



In making these colorimetric determinations of pH a very small 

 amount of fluid should be used for each test because it has to be dis- 

 carded after the indicator solution has been added to it. Dilutions 

 should be made with distilled water only, and all test tubes or other 

 containers employed for these tests should be given several rinsings 

 with distilled water before re-use. 



Containers for Preserving Fluids 



Only glass or other nonmetallic containers should be used for the 

 preserving fluids employed in this process. The four types of containers 

 described below have been found to be convenient for the several 

 purposes for which they are needed. 



1. Dispensing containers. — For storing working quantities of the 

 various types of preserving fluids to be applied to flattened specimens, 

 glass jars of 8-ounce or 16-ounce capacity are satisfactory. Glass- 

 topped preserve jars are especially suitable, but jars with screw caps 

 may be used if the caps are provided with Vinylite liners or with water- 

 proof paraffin-coated card liners. 



