432 On the Chemical Composition of Phosphatic Minerals 
of a solution of crude phosphate of alumina in sulphuric acid, 
recommend to mix the finely powdered mineral with a sufficient 
quantity of sulphuric acid to render the phosphate of alumina 
and iron soluble. A small quantity of the solution thus 
obtained and diluted with some water, these gentlemen recom- 
mend to be poured into foul town sewage, and at the same time 
to add a little milk of lime, when an immediate flocculent 
precipitate is formed, which readily settles at the bottom 
of the precipitating-tank, carrying down with it all the sus- 
pended organic matter and a portion of the soluble organic 
impurities of town sewage, and leaving the supernatant liquid 
almost colourless, fairly clear, and inoffensive to smell. 
The dried sewage deposit consists of a mixture of precipitated 
phosphates of iron, alumina, and lime, and contains also more 
or less organic matters (yielding ammonia on decomposition), 
and fine sand, and similar mineral insoluble impurities present 
in town sewage. It constitutes a useful artificial manure. 
The following are the results which I obtained from the 
analysis of four samples of Redonda phosphate : — 
Composition of Four Samples of Eedonda Phosphate. 
No. 1. 
Ko. 2. 
No. 3. 
No. 4. 
Moisture and water of combination 
23-23 
36-95 
36-38 
3-44 
21-15 
37-04 
32-26 
9-55 
27-70 
19-40 
25-65 
27-25 
24-20 
38-52 
35-33 
1-95 
100 00 
100-00 
100-00 
100-00 
* Corresponding to tribasic pbospbate "1 
80-66 
80-86 
42-35 
84-09 
The samples Nos. 1, 2, and 4, it will be seen, were very rich 
in phosphoric acid ; No. 3 represents the composition of an 
unusually poor sample of Redonda phosphate. 
16. Alta Vela Phosphate. 
Alta Vela Rock phosphate is found on the small island of 
Alta Vela near St. Domingo, and is another form of crude 
phosphate of alumina, which may be used for the same purposes 
lor which Redonda phosphate is employed. It appears to vary 
in composition to a greater extent than Redonda phosphate. 
The following is an analysis of a sample of inferior Alta Vela 
phosphate : — 
