Final Evaporation Control in reservoirs

9.2
 
Indicator Oils 
For effective retardation of evaporation, the molecular film formed should develop 
adequate pressure. In most cases the initial film pressure is in the range of 20-30 
dyne/cm and equilibrium pressure of 40 dyne/cm can be achieved with appropriate 

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88
dosage. For testing the pressure of WER film, oils of known spreading pressure 
(indicator oils) are used. The surface pressure developed by certain indicator oils are 
given in Table 9.4. 
TABLE 9.4 Surface Pressure of Indicator Oils at 21 °C 
S. No
Indicator Oils
Surface pressure developed at 21 
°C (dyne/cm)
1.
Shell Ensis fluid 256
40 
2.
Undocylic acid
34.5 
3.
Hexadecyl acetate
34.4 
4.
Oloic acid
30.0 
5.
Octadecyl acetate
24.0 
6.
Shell Vitrea Oil 21
24.0 
7.
Triolein
22.0 
8.
Lauric acid
21.0 
9.
Castor oil
17.0 
10.
Ethyl Pholometite
16.5 
11.
Shell Vitrea oil 13
16.0 
12.
Shell H.S.D.
13.0 
13.
Triorozyl phosphate
10.0 
14.
Myrystic acid
11.0 
15.
Palmitic acid
8.5 
16.
Carbon disulphide
2.3 
17.
Steanic acid
1.5 

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89
10.0
 
MERITS 
AND 
DEMERITS 
OF 
SOLID 
AND 
EMULSION FORM OF WERs 
The Acilol TA-1618 is available in solid lump form as well as in emulsion form. In 
Saurashtra region of Gujarat State, evaporation control works have been carried out 
extensively with Acilol-1618 in powder form and emulsion form during 1985-88. The 
WER “Linoxyd CS-40” is available in emulsion form only. This WER was used for 
evaporation control in Maharashtra during 1977-80 and 1983-85. The merits and demerits 
of using powder and emulsion form for evaporation control on the basis of their use in 
Gujarat and Maharashtra have been reported by the Directorate of Irrigation Research and 
Development, Pune and are given below.