Solution depression

One mole of solute dissolved in 1000 g of solvent (to produce a 1 molal solution) depresses the freezing point by the molal freezing point depression constant (X/). The degree to which the freezing point of any solution is depressed (compared to that of the pure solvent) is directly proportional to the molality of the solute present. 

Pm Partial pressure of water vapor due to solution depression (td - tw), mmHg... 

Solute depression of the melting point can also occur due to the dissolution of gases in water. Ordinarily the solubility of ordinary gases is so small that this depression is not easily measurable. However, some gases, such as CO2, have a far higher solubility in water and solute depression can be easily measured with a thermistor. 

Since Atfvap > AHfa%, it follows that the addition of a solute depresses the freezing point to a greater extent than it raises the boiling point ... 

Lactic acid Liquid 230 -900 10 % solution Depressing the floatation of mica when using FeS Depressing mica... 

Ferrous sulfate and ferric sulfate Granularity 45-900 10 % solution Depressing sulfide ores Depressing the floatation of dissociated Au Activating quartz, increasing the recovery of PbS depressed by chromate improving the separation of nonmetallic ores ... 

Experiments carried out by Keir, van Rooyen and Pryor have clarified the variable behaviour of the Al-Zn couple in chloride solutions. Using high-purity aluminium and zinc electrodes of equal size coupled together in sodium chloride solution, it was found that zinc is initially anodic to aluminium but that within one day the polarity of the couple reverses and remains as such subsequently (Fig. 1.70). This reversal in polarity appears to be due to the accumulation of Zn in solution. Accordingly, with decrease in distance between the electrodes, and in solution-volume electrode-area ratio, the polarity reversal occurs much more rapidly. The accumulation of Zn in solution depresses the potential of the aluminium from an initial value of about -0-5 V to a final open-circuit value of about —1-0 V (vj. S.H.E.). The corrosion rates of both the aluminium and the zinc electrodes are greater than in the absence of bimetallic contact, but the corrosion of the aluminium is changed from the characteristic pitting, usually observed in nearly neutral chlorides, to a desirable mild uniform attack. The polarity reversal is not... 

Addition of membrane fragments to 9-AA solutions depresses their fluorescence, because of the deposition of probe molecules in the diffuse electric layer, which borders the membrane surface. The deposited probe molecules are displaced back to the bulk phase by metal cations, with a concomitant rise in the fluorescence. This is illustrated in Fig. 1, where the maximal cation-released fluorescence (Fmax), divided by the fluorescence at submaximal cation concentrations (F) is plotted against the logarithm of the metal cation concentration. Curves for Nostoc, Phor-midium and spinach thylakoid fragments are illustrated. 

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