84 



ALKALIMETRY 



about 6,000 grains of water ; pour upon them about 2,000 grains of water, and shako 

 until dissolved. Add now sulphuric acid thereto ; this will produce a smart effer- 

 vescence, and in all probability a deposit of sulphate of potash. Wo say in all 

 probability, because it is clear that if the potash in question is largely adulterated 

 with soda, or was altogether nothing else than carbonate of soda, as has occasionally 

 happened, it is evident that no deposit of sulphate of potash would take place ; and 

 yet, as it is necessary to the success of the operation that the liquor should contain an 

 excess of this latter salt, a certain quantity of it previously reduced to fine powder 

 must in that .case bo purposely added to the solution. 



71. After the disengagement of gas has ceased, it is necessary to pour the dilute acid 

 cautiously, and only drop by drop, until the neutralising point is correctly hit, which 

 will be known as usual by testing with litmus-paper. But if, by accident, too much 

 acid have been used, -which is known by the reddening of the litmus-paper, the slight 

 overdose may be neutralised by adding a small quantity of "weak solution of potash. 



72. As this reaction produces heat, it is necessary to lower the liquor do-wn to the 

 temperature of the atmosphere, decant in a filter placed over the glass cylinder, and 

 fill it up to the scratch 3,000, by -washing the residue on the filter with a saturated 

 solution of sulphate of potash, exactly as described in 63. 



73. The glass cylinder being properly filled up to the scratch, remove the funnel, 

 close the orifice of the glass cylinder -with the palm of the hand, and shake the -whole 

 violently ; holding the natrometer, which should be perfectly clean, by its upper 

 extremity, slowly immerse it in the solution. If the potash under examination bo 

 pure, the pink scale will indicate the degree of temperature at which the experiment 

 has been made, taking the under line as the true level of the liquid ; but if, on the 

 contrary, it contains soda, the pink scale of temperatures will indicate a few degrees 

 more than the real temperature, and this surplus number of degrees, being compared 

 with those of the soda scale contiguous to it, on the opposite side, will express the 

 per-centage of soda present in the sample. 



74. For example : Suppose the experiment to have been made at +12 Centi- 

 grade, and to have given a solution marking 25 on the pink scale of temperatures of 

 the natrometer, that is 13 more than the real temperature ; looking, therefore, at 

 number 13 on the pink scale of temperature, it -will be seen that the number exactly 

 opposite on the soda scale, and corresponding to it, is 4, -which indicates that tho 

 sample of potash examined contains 4 per cent, of soda. 



It is important to bear in mind that all commercial potashes contain naturally a 

 small quantity of soda, which quantity, in certain varieties, may even be considerable ; 

 it is only when the proportion of soda is more considerable than that -which is 

 naturally contained in the species of potash submitted to analysis, that it should be 

 considered as fraudulently added. The following Table, published by M. Pesier, shows 

 the average composition of the principal varieties of potash found in commerce, -when 

 in an unadulterated state : 



Average Composition of Potashes. 



1 In the impossibility of estimating exactly the loss by calcination, and the quantity of oxide of 

 potassium in the caustic state (hydrate of potash), we have reduced the potash to the state of car- 

 bonate, to make comparison more easy. 



