potassium dichromate solution is 

 pipetted in. This is evaporated to dry- 

 ness overnight at 80° to 85° C. After 

 drying, 0.500 gnn. of dried powdered 

 sediment is added and 10 ml. of con- 

 centrated sulfuric acid is drawn into the 

 tube from a burette. The sample and 

 solution are heated to about 1 75° C. with 

 constant stirring over a Bunsenburner 

 in a period of 90 seconds. The mixture 

 is air cooled to 100° C. and then cooled 

 in running cold water. The contents of 

 the tube are poured into about 50 ml. of 

 distilled water and the tube rinsed until 

 the volume of liquid is about 1 50 ml. Five 

 gms. of sodium fluoride is added and the 

 mixture titrated against ferrous ammo- 

 nium sulfate using diphenylamine indi- 

 cator. Three drops of indicator are suf- 

 ficient. The end point is a slow but 

 distinct change from blue to green. 



Blank determinations should be run 

 together with each group of three or 

 four samples. 



Sediment type 



Reagents : None required. 



Procedure : Following the mechanical 

 analysis of the distribution of grain 

 sizes in a sediment sample, the per- 

 centages of grains of clay, salt, sand, 

 and gravel size are determined follow- 

 ing Wentworth's classes of size grades 

 (1922). A textural type name is then 

 determined using the graphical method 

 of locating the position of the individual 

 sample in a tetrahedron whose quoins 

 represent 100 percent clay, silt, sand 

 or gravel (fig. 3). Except in rare in- 

 stances, marine sediments are usually 

 composed of no more than three com- 

 ponents. For this reason, a simple 

 triangle diagram is sufficient for the 

 classification procedure. If a sediment 

 sample is composed of 5 percent silt, 

 65 percent sand and 30 percent gravel, 

 then the position of this combination 

 on the triangle shown in figure 3 would 



100% 



100% 



100% 



Figure 3.-- leirahedroii for determining textural types. 



16 



