ALKALIMETRY 



time, and not one immediately prepared for the purpose, because sulphate of potash 

 in dissolving produces a certain amount of cold, which would create delay, since it 

 would be necessary to wait until the temperature of the mass had become the same as 

 that of the air. 



64. The liquor occupying 3,000 water-grains' measure in the cylinder should bo 

 next rendered homogeneous by stirring it well, after which the natromotor may bo 

 immersed in it. The natrometor is simply an areometer of a peculiar construction, 

 provided with two scales : the one of a pink colour shows the degrees of temperature, 

 and indicates, for each degree of the Centigrade thermometer, the level at which a 

 solution saturated with pure sulphate of potash would stand ; on the other scale, 

 each degree represents 1 per cent, of soda (oxide of sodium), as represented iufy. 34. 

 65. The of the two scales coincide with each other. If the experiment 

 34 take place at the temperature of 0, the quantity of soda will be directly 

 determined by observing the number of degrees on the soda scale ; but if 

 the experiment be performed at 25, for example, it will be seen that the 

 point at which the instrument would sink in a liquor saturated with pure 

 sulphate of potash corresponds to 

 T 5 5 th of soda, and, in this case, it 

 is from this point that the of the 

 soda scale should be supposed to 

 begin, which is easily accomplished 

 by a simple subtraction, as will be 

 seen presently. 



66. Experiment having shown 

 that the degrees of soda cannot bo 

 equidistant, but that, on the con- 

 trary, they become smaller and 

 smaller as the quantity of soda in- 

 creases, the number of degrees of 

 soda are obtained as follows: 

 From the number of degrees of 

 temperature now indicated on the 

 pink scale of the natrometer, sub- 

 tract the number of degrees of 

 temperature indicated by an or- 

 dinary thermometer at starting ; 

 then look at the soda scale for the 

 number of soda degrees which cor- 

 respond to the number of degrees 

 of temperature left after subtrac- 

 tion, and each of the soda degrees, 

 beginning from the of the na- 

 trometer, represents 1 per cent. 



67. For example: Suppose the 

 experiment to have been made at 

 starting, and as indicated by an 

 ordinary thermometer, at + 20 



Centigrade, and that the level of the solution is now found to stand at 59 on the 

 pink scale of temperature of the natrometer, then by deducting 20 (the original 

 temperature) from 59 (number of degrees indicated by the floating point on the pink 

 scale of temperatures of the natrometer), there remains, of course, 39. Draw the 

 instrument out, and looking now on the said pink scale for 39, there will be found 

 exactly opposite, on the soda scale, the number 13, which number signifies that the 

 potash under examination contains 13 per cent, of soda (oxide of sodium). 



68. As the deposit of sulphate of potash separated by filtering might retain some 

 sulphate of soda, it is advisable, in order to avoid all chance of enror, -to wash it with 

 a saturated solution of sulphate of potash, adding as much of it as is necessary to 

 bring the whole mass of the liquor up to the mark 3,000 water-grains' measure, in 

 which the natrometer being again immersed, the minute quantity of soda indicated 

 should be added to the per-centage found by the first operation. 



69. If a great degree of accuracy is required, the fractions of degree of the instru- 

 ment must be taken account of ; otherwise they may be neglected without the result 

 being materially affected, since 3 degrees of the scale of temperature correspond only 

 to about 1 per cent, of soda. 



70. For commercial purposes, the process may be slightly varied, as follows : 

 Take 500 grains of a fair average sample of the potash to be examined, previously 

 reduced to powder, and throw them into a flask, A (fig. 35), capable of containing 



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