Potash alum sulphurated

About 2 gm. benzyl iodide are weighed into a flask and then 50 ml. 20% alcoholic potash solution are added and the mixture refluxed for about an hour. At the completion of the saponification the contents of the flask are allowed to cool and then transferred to a 500-ml. flask and made up to volume with water. 100 ml. of the resulting solution are placed in a distillation flask and distilled in steam after adding 10 gm. ferric ammonium alum and acidifying with sulphuric acid. By this treatment, the ferric salt is converted to the ferrous condition, liberating iodine which is distilled over into 5% potassium iodide solution. At the end of the distillation, the free iodine in the potassium iodide solution is titrated with a decinormal solution of sodium thiosulphate. From this, the amount of iodine and so the quantity of benzyl iodide in the sample may be calculated. 

And this abbreviated expression contains, in a line, in addition to the general information concerning alum printed abov more information as to details than could be given in a page of print. It informs us, for example, that alum contains 4 eq. sulfuric acid, of which 1 is combined with 1 eq. of potash, and 3 with 1 eq. of alumina that alumina is a sesquioxide of aluminum that 1 eq. alum contains 1 eq. potassium, 2 eq. aluminum, 4 eq. sulphur, 24 eq. hydrogen, and 40 eq. oxygen, c. c. c. 

In a paper on the analysis of mineral water from a place near an alum mine in Italy Lavoisier reports that the compound of alumina and sulphuric acid does not crystallise well, that to form true alum it is necessary, as M. Marggraf observed , to add fixed alkali (potash), and that the base of alum is not a simple earth, as all chemists have hitherto supposed, but a compound of an earth, with a third or half its weight of fixed alkali... as already remarked by M. Macquer (Marggraf). It is probable that alums could be formed with soda, magnesia (. ), lime, and perhaps ammonia. 

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