Double salt interval

From what has been said, it is evident that when the formation of a double salt can occur, three temperature intervals can be distinguished, viz. the single-salt interval, the transition interval, and the double-salt interval. When the temperature lies in the first interval, evaporation leads first of all to the crystallisation of one of the single salts, and then to the separation of both the single salts together. In the second temperature interval, evaporation again leads, in the first place, to the deposition of one of the single salts, and afterwards to the crystallisation of the double salt. In the third temperature interval, only the double salt crystallises out. This will become clearer from what follows. 

Transition Interval,—Fig. 115 will also render intelligible a point of great importance in connection with astracanite, and with double salts generally. At temperatures between those represented by the points B and X, the double salt when brought in contact with water will be decomposed with separation of sodium sulphate. Above the temperature of the point X, however, the solution of the pure double salt is stable, because it can still take up a little of either of the components. At temperatures, then, above that at which the solution in contact with the double salt and the less soluble single salt, contains the single salts in the ratio in which they are present in the double salt,... 

In those cases where the double salt is the stable form below the transition point, the transition interval will extend downwards to a lower temperature. Fig. 115 will then have the reverse form. 

Summary.— With regard to double salts we have learned that their formation from and their decomposition into the single salts is connected with a definite temperature, the transition temperature. At this transition temperature two vapour pressure curves cut, viz. a curve of dehydration of a mixture of the single salts and the solubility curve of the double salt or the dehydration curve of the double salt and the solubility curve of the mixed single salts. The solubility curves, also, of these two systems intersect at the transition point, but although the formation of the double salt commences at the transition point, complete stability in contact with water may not be attained till some temperature above (or below) that point. Only when ike temperature is beyond the transition interval will a double salt dissolve in water without decomposition (e.g. the alums). 

Formation of Double Salt— We have already learned in the preceding chapter that if the temperature is outside the transition interval, it is possible to prepare a pure saturated solution of the double salt. If we suppose the double salt to contain the two constituent salts in equimolccular proportions, its saturated solution must be represented by a point lying on the line which bisects the angle AOB e.g. 

If the formation of double salt is possible, but if the temperature lies within the transition interval, the relations will be represented by a diagram like Fig. 126. Isothermal evaporation of the solution X will lead to the deposition of the component A, and the composition of the solution will alter in the direction DE at the point E, the double salt will be formed, and the composition of the solution will remain... 

Lastly, if the temperature lies outside the transition interval, isothermal evaporation of an unsaturated solution of the composition X (Fig. 127) will lead to the deposition of pure double salt from beginning to end. If a solution of the composition Y is evaporated, the component A will first be deposited and the composition of the solution will alter in the direction of E, at which point double salt will separate out. Since the solution at this point contains relatively more of A than is present in the double salt, both the double salt and the single salt A will be deposited on continued evaporation, in order that the composition of the solution shall remain unchanged. In the case of solution Z, first component B and afterwards the double salt will be deposited. The result will, therefore, be a mixture of double salt and the salt B (congruently saturated solutions). 

As has already been pointed out, the formation of racemic compounds from the two enantiomorphous isomerides, is analogous to the formation of double salts. The isothermal solubility curves also have a similar form. In the case of the latter, indeed, the relationships are simplified by the fact that the two enantiomorphous forms have identical solubility, and the solubility cur 7-es are therefore symmetrical to the line bisecting the angle of the co-ordinates. Further, with the exception of the partially racemic compounds to be mentioned later, there is no transition interval. 

Partially racemic compounds, —In this case we are no longer dealing with enantiomorphous forms, and the solubility of the two oppositely active isomerides is no longer the same. The symmetry of the solubility curves therefore disappears, and a figure is obtained which is identical in its general form with that found in the case of ordinary double salts (Fig. 129). In this case there is a transition interval. 

Transition Interval.—double salt, we learned (p. 242), when brought in contact with water at the transition point undergoes partial decomposition with separation of one of the constituent salts and only after a certain range of temperature (transition interval) has been passed, can a pure saturated solution of the double salt be obtained. A similar behaviour is also found in the case of reciprocal salt-pairs. In the case of each salt-pair there will be a certain range of temperature, called the transition interval, within which, if excess of the salt-pair is brought into contact with water, interaction will occur and one of the salts of the reciprocal salt-pair will be deposited. For the salt-pair which is stable below the transition point, the transition interval will extend down to a certain temperature below the transition point and for the salt-pair which is stable above the transition point, the transition interval will extend up to a certain temperature above the transition point. Only when the temperature is below the lower limit or above the upper limit of the transition interval, will it be possible to prepare a solution saturated only for the one salt-pair. In the case of ammonium chloride and sodium nitrate the lower limit of the transition interval is 5 5 , so that above this temperature and up to that of the transition point (unknown), ammonium chloride and sodium nitrate in contact with water will give rise to a third salt by double decomposition, in this case to sodium chloride. ... 

Into a 1-litre beaker, provided with a mechanical stirrer, place 36 - 8 g. (36 ml.) of aniline, 50 g. of sodium bicarbonate and 350 ml. of water cool to 12-15° by the addition of a little crushed ice. Stir the mixture, and introduce 85 g. of powdered, resublimed iodine in portions of 5-6 g, at intervals of 2-3 minutes so that all the iodine is added during 30 minutes. Continue stirring for 20-30 minutes, by which time the colour of the free iodine in the solution has practically disappeared and the reaction is complete. Filter the crude p-iodoaniline with suction on a Buchner funnel, drain as completely as possible, and dry it in the air. Save the filtrate for the recovery of the iodine (1). Place the crude product in a 750 ml. round-bottomed flask fitted with a reflux double surface condenser add 325 ml. of light petroleum, b.p. 60-80°, and heat in a water bath maintained at 75-80°. Shake the flask frequently and after about 15 minutes, slowly decant the clear hot solution into a beaker set in a freezing mixture of ice and salt, and stir constantly. The p-iodoaniline crystallises almost immediately in almost colourless needles filter and dry the crystals in the air. Return the filtrate to the flask for use in a second extraction as before (2). The yield of p-iodoaniline, m.p. 62-63°, is 60 g. 

Using this technique, pool sizes of cholic acid and chenodeoxycholic acid have been estimated to be similar and around 1.0 to 1.5 g each in healthy subjects, with the total bile acid pool amounting to 2 to 4 g (H18, LIO, VIO). Cholic acid turnover is more rapid than for chenodeoxycholic acid, and the rate of hepatic synthesis of cholic acid (300 to 400 mg/day) is therefore approximately double that for chenodeoxycholic acid (150 to 200 mg/day) (H18, VIO). In the steady state, total bile acid synthesis by the liver should equal bile acid loss in the feces, which is around 400 mg/day. Some studies have found that estimates of bile acid synthesis by the isotope dilution technique give values that are higher than those obtained by direct chemical measurement of fecal bile salts (S45), but good agreement has recently been claimed between the two methods (DIO). ITie Lindstedt technique for measuring bile acid turnover and pool size has been modified so that only one bile sample need be collected after intravenous administration of the labeled bile acid. These modified methods measure either pool size alone (D9) or pool size and turnover if both and bile acid are administered at an interval of 24 hours apart (V6). 

Electrodes were made from two-barrel borosilicate glass tubing with filaments (WPI). One barrel was filled with 3 M KCl (2-10 MU) for stimulation and recording. For microejections, the other barrel was filled with 5% Lucifer Yellow (Lucifer Yellow CH, lithium salt. Molecular Probes) in 150 mM LiCl or with lOmM Alexa fluor 488 (hydrazide, sodium salt. Molecular Probes) in 200 mM KCl. When the double-barrel microelectrode was inserted into a cell, dye ejection was accomplished with 100-msec negative current pulses (1-50 nA) delivered through the dye-filled barrel and applied for 1-5 min at 100-msec intervals. After dye ejection the tissue was fixed. 

The fate of RF-RNA in . coli was studied by fractionation of the isolated RNA by LiCl precipitation. RF-RNA is soluble in solutions of 1.0 and 1.5 M LiCl. Single-stranded RNA and double-stranded RNA with attached single-stranded RNA (RI-RNA) precipitate in 1.5 M LiCl at —12° C. More label was found in the LiCl-soluble fraction in cell samples which were incubated for longer time intervals after exposure to RF-RNA. The amount of labeled RF-RNA converted from a salt-soluble to an insoluble RNA in a given time interval varied from experiment to experiment, dep nding on the amount of input RNA (Koch and Vollertsen, unpublished). With small amounts of RF-RNA (less than 1 (xg/g of cells) 50% of the RF-RNA label was found in a LiCl-sedimentable form. With more RF-RNA (30 (xg/g of cells), the ratio of input counts in LiCl supernatant fluid to LiCl sediment was 9.2 1 at 20 min and 4.6 1 at 120 min (Table 11). 

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