26 



stand, a dinner plate or porcelain slab, half ounce of ferrocyanide 

 of potassium in powder, half pint of acetic mixture, half pint of 

 caustic potash 10 per cent, solution, half pint of acetic acid and, 

 half pint or a pint of the standard solution of uranium nitrate, one 

 decern to be exactly equal to -Oo of a grain of phosphoric acid, 

 or •10915 of a grain of bone earth made soluble. This solution 

 must be kept in a well stoppered bottle in a dark place, the 

 bottle must be well shaken before using the solution, and every 

 care must be taken that it does not get altered in strength by 

 the addition of water or any other fluid. 



The first thing to be done in analysing a superphosphate is 

 to get a fair sample, this is best accomplished by taking a good 

 handful out of several bags and well mixing in a basin, takings 

 care to breakdown all lumps. When it is thoroughly well mixed 

 about a table spoonful is to be taken out and well beaten and 

 ground in the mortar till it is in a very finely divided state, it will 

 generally get in a creamy ur pasty state during this operation. 



Exactly one hundred grains of this sample are then to be 

 very carefully weighed out. This is best done by hanging the 

 scales up to the ring of the retort stand, putting a watch glass 

 and the weights (if the apothecaries' weights are used, the dram 

 and two scruples will make up one hundred grains) in one pan, 

 and exactly counterpoising the other with small shots and pieces 

 of paper, the weights are then to be taken out of the watch glass 

 and enough superphosphate added to exactly counterpoise the 

 shots. 



The weighed superphosphate is then to be carefully trans- 

 ferred to the clean mortar and well ground with a little cold 

 •water, allowed to settle about a minute and then poured down 

 the pestle on to a filter paper, which must have been folded and 

 placed in the glass funnel and wetted. The glass funnel should 

 be suspended in one of the rings of the retort stand with its 

 stem just in the mouth of the 500 decern flask. If the solution 

 should run through thick at first it must be returned to the filter 

 till it comes through clear and bright. This grinding with cold 

 water and pouring off must be repeated about three times and all 

 the superphosphate must be washed out of the mortar on to 

 the filter. When all the solution has run through, the filter is to 

 be filled up with clean water about twice, waiting each time till 

 the filter is empty, when this has all passed through we may be 

 sure that all the soluble phosphate is in solution. In all these 

 grindings and washings only enough water should be used to fill 

 the 500 decern flask three parts full. 



Our solution now contains all the soluble phosphate of lime 

 with probably some iron if a mineral superphosphate, now add 

 a small piece of blue litmus paper to the flask, the acid phos- 

 phate quickly turns it red, now add some caustic potash till the 

 paper is again quite blue, mix thoroughly by shaking the flask, this 

 makes our solution very thick, having thrown down all the phos- 

 phate of lime and iron. Now add acetic acid till the turbidity is 



