1868. ] Chemistry. 231 
showed that as much as 44 per cent. of the urea might be lost in 
this way. These two sources of error may be avoided by leaving 
out the carbonate of soda, evaporating at a low temperature, and 
drying at 100° C. A little water will be left behind in this 
way, but it will be chemically combined, and may be fairly con- 
sidered part of the solid constituents. The differences of weight in 
residues dried at these different temperatures was shown by a few 
examples. Thus, a residue which dried at 100°, weighed 27-02, 
when heated to 120°—130°, weighed 26°54. Another, dried at 
100°, weighed 26°70, and at 120°—130°, 26:20. Before, however, 
a residue is ignited to determine the organic matter, the water must 
be expelled by carrying the heat to the higher temperature. 
2. To determine the organic and volatile matters, the residue 
is heated to dull redness. By this the carbonates of lime and 
magnesia are causticized, and must be recarbonated by means of 
carbonic acid water; the addition of which, and the redrying must 
be repeated until the weight of the residue ceases to increase. In 
this process there are also two sources of error. The organic matter 
may not be entirely destroyed. When, for example, urea is evapo- 
rated with sodie carbonate, the loss on ignition represents but a 
small part of the urea in the original residue. Sometimes also after 
recarbonating an ignited residue it weighs more than before ignition. 
In any case a loss on ignition may represent organic matter, or it 
may represent mineral nitrites and nitrates, while the organic matter 
may remain. 
3. To ascertain the amount of oxygen required to oxidize 
organic matter, a solution of permanganate of potash is employed. 
This process Dr. Frankland said is utterly untrustworthy, many 
organic substances refusing to be completely oxidized by this means. 
In the cases of urea and hippuric acid, for example, the oxygen 
consumed represented only one-fiftieth of that required by theory. 
4. To determine nitrous and nitric acids, Dr. Pugh’s method 
has been generally followed, but Messrs. Chapman and Schenck 
have shown that many organic substances affect the result. 
5. To estimate ammonia the water is usually distilled with 
baryta or carbonate of soda, and the ammonia determined in the 
distillate either by neutralization or Nessler’s test. When, how- 
ever, urea is present, ammonia may be liberated, which will be 
estimated as free. After this criticism of the usual processes, 
Dr. Frankland made some suggestions for their improvement. To 
determine the amount of solid ingredients, he recommended that 
half a litre, or a litre, of the water should be evaporated as rapidly 
as possible, and the residue dried at 100°. Our space will not 
allow us to describe the particular manner by which Dr. Frankland 
determines the amount of organic carbon and nitrogen from which 
he deduces the amount of organic contamination. We may say 
