FACS

SATURATED LIQUID MOLAR VOLUME, CC/GR-MOLE ZERO PRESS REF FUGACITY IF 1VAP.LE.2 OR VA OR PRESS IP lVAP.f O.3 K-FAC TOR... 

The location of the crossing seam (or seam) for an X3 system is established from the requirement that /-ab = rec = r c, where j-ab, rec, and fAc are the interatomic distances. Since the goal are the the geometric properties produced by this seam, hyperspherical coordinates (p,0,atomic masses are equal, say iiiB = me, the seam is defined [5] by... 

Substitution can take place by the S l or the 8 2 mechanism elimination by El or E2 How can we predict whether substitution or elimination will be the principal reac tion observed with a particular combination of reactants The two most important fac tors are the structure of the alkyl halide and the basicity of the anion It is useful to approach the question from the premise that the characteristic reaction of alkyl halides with Lewis bases is elimination and that substitution predominates only under certain special circumstances In a typical reaction a typical secondary alkyl halide such as iso propyl bromide reacts with a typical Lewis base such as sodium ethoxide mainly by elimination... 

MAFF (1979), Interim Report on the Review of the Colouring Matter in Food Regulations, FAC/REP / 29, Ministry of Agriculture, Eisheries and Eood, Eood Additives and Contaminants Committee, HMSO, London, 1973. 

Maintenance Available Chlorine. AH chlorine saniti2ers provide free available chlorine (FAC), ie, HOCl + C10 . Available chlorine is a... 

Superchlorination typically refers to a dding FAC equal to 10 x ppm CAC, whereas shock treatment generally involves addition of 10 ppm FAC. The frequency of superchlorination or shock treatment depends on bather load and temperature. Calcium hypochlorite, because of its convenience, is widely used for superchlorination and shock treatment. Sodium hypochlorite, LiOCl, or chlorine gas are also used. Chloroisocyanurates are not recommended since their use would result in excessive cyanuric acid concentrations. 

The pH is measured colorimetricaHy with phenol red indicator. High FAC causes lower pH rea dings due to bleaching of the indicator and resultant HCl formation. The pH of pool water is readily controlled with inexpensive chemicals. Hydrochloric acid solution or sodium bisulfate lower it, whereas sodium carbonate raises it. Since acid addition neutralizes a portion of the alkalinity, this must be replenished if the alkalinity drops below the minimum. By contrast, pH adjustment with carbon dioxide does not affect alkalinity. 

The error is approximately equal to the FAC at pH 7.2—7.8. However, it is significant only at high FAC, eg, during superchlorination or shock treatment. 

At 25°C, pH 7.5, 1.5 ppm FAC, and 25 ppm cyanuric acid, the calculated HOCl concentration is only 0.01 ppm. Although the monochloroisocyanurate ion hydrolyzes to only a small extent, it serves as a reservoir of HOCl because of rapid hydrolysis. Indeed, this reaction is so fast that HClCy behaves like FAC in all wet methods of analysis. Furthermore, since HClCy absorbs uv only below 250 nm, which is filtered out of solar radiation by the earth s atmosphere, it is more resistant to decomposition than the photoactive C10 , which absorbs sunlight at 250—350 nm and represents the principal mode of chlorine loss in unstabilized pools (30). As Httie as 5 ppm of bromide ion prevents stabilization of FAC by cyanuric acid (23) (see also Cyanuric and ISOCYANURIC acids). 

Based on the above equilibria, the concentration of HOCl in the normal pH range varies inversely with the total concentration of cyanurate. Increased concentration of cyanuric acid, therefore, should decrease the biocidal effectiveness of FAC. This has been confirmed by laboratory studies in buffered distilled water which showed 99% kill times of S.faecalis at 20°C increasing linearly with increasing cyanuric acid concentration at constant av. Cl at pH 7 and 9 (45). Other studies in distilled water have found a similar effect of cyanuric acid on kill times of bacteria (46—48). Calculations based on the data from Ref. 45 show that the kill times are highly correlated to the HOCl concentration and poorly to the concentration of the various chloroisocyanurates, indicating that HOCl is the active bactericide in stabilized pools (49). 

Pseudomonas that cause skin infections, within 30 s by 2 ppm FAC at pH 7.4 (62). In a series of tests under stabilized conditions (50—100 ppm cyanuric acid), an initial concentration of 3 ppm FAC could not provide water that met the NSPI standards for bacteria or the maintenance of at least a 2 ppm FAC residual. Increasing the initial FAC to 4 ppm resulted in the bacterial criteria being met 100% of the time even when the FAC residual fell below 1 ppm. For heavy bather loads an initial FAC > 4 ppm is recommended. 

For optimum disinfection in swimming pools, the pH is maintained in the 7.2 to 7.6 range where HOCl represents 69—47% of the FAC. By contrast, the HOBr fraction varies from 97 to 93%. Nevertheless, the bactericidal effectiveness of HOCl is greater than that of HOBr below pH 8 on a molar basis (8). However, above pH 8 the superiority of HOCl is overcome by the fact that the concentration of C10 exceeds that of HOCl above pH 7.5, whereas the concentration of HOBr stiU exceeds that of BrO up to pH 8.7. Hypochlorous acid is a better viricide than HOBr, but HOBr is more effective against certain algae (9). 

---