220 - B. Silliman, Jr., on the 
infusoria, usually present in the sweet waters of our ponds and 
rivers. Water which will not support the life of these delicate 
creatures is not fit for human use. Fora list of these, see the 
copy of his letter in the report in question. 
Only Nos. 1 and 11 were decidedly hard waters. The others 
were generally quite soft. 
The general course of analysis was in most respects, similar to 
that usually pursued. A full qualitative examination was first 
made, to determine the number and eer ebundinek: of 
the foreign matters. 
This examination showed that the waters were all neutral ex- 
cept, Nos. 5, 6, 9, 10, and 11, which contained an appreciable 
quantity of crenic and apocrenic acids. The carbonic acid was 
determined by Berzelius’s mode, on a separate quantity, and the 
sulphuric acid was subsequently estimated on the same portion. 
- No ammonia was detected in any of them. 
The solid contents were determined by evaporation to a small 
bulk, of a carefully measured standard gallon of each, in capacious 
glass flasks, and the evaporation was completed in counterpoised 
capsules of platina or porcelain. The subsequent. ignition of these 
capsules gave us the amount of matters volatile at redness. ‘The 
ultimate analysis of the solid contents was divided into two ais 
that soluble in boiling water, and the insoluble residue. 
The phosphoric acid was determined by a re-solution of the 
ammoniacal precipitate of alumina, iron, &c. in pure acetic acid. 
If an insoluble residue remained, it was collected, weighed, and 
then separately analyzed to determine with entire certainty the 
presence of phosphoric acid. For this purpose the supposed 
phosphates (of alumina and iron) were fused with one part of 
silica and six parts of pure carbonate of soda, for half an hour, in 
acrucible of platinum. The fused mass, treated with water, 
was filtered, and the silicic acid removed from the filtrate by di- 
gestion with carbonate of ammonia and evaporation to dryness. 
The neutralized filtrate was then treated with nitrate of silver, 
which promptly threw down the characteristic precipitate of yel- 
low tribasic phosphate of silver, blackening by light, and wholly 
soluble in dilute nitric acid. This is the method advised by Ber- 
zelius for the separation of alumina from phosphoric acid, and 
no better proof can be required of its presence. ‘The occurrence 
of phosphoric acid in water has generally been overlooked, be- 
nsuspecte: “Iehas escaped under the general tile of si 
Ce Nici ee ee oe a eel tbe 5 
