FOOTNOTES:

[5] It is best to use this form with a glass stopcock, or with an
india-rubber tube and clip, after the manner of a Mohr's burette.




CHAPTER VI.

RE-AGENTS.--ACIDS, ETC.


~Acetic Acid~, H[=A=c] or C_{2}H_{4}O_{2}. (sp. gr. 1.044, containing 33
per cent. real acid).--An organic acid, forming a class of salts,
acetates, which are for the most part soluble in water, and which, on
ignition, leave the oxide or carbonate of the metal. It is almost always
used in those cases where mineral acids are objectionable. To convert,
for example, a solution of a substance in hydrochloric acid into a
solution of the same in acetic acid, alkali should be added in excess
and then acetic acid. Many compounds are insoluble in acetic acid, which
are soluble in mineral acids, such as ferric phosphate, ferric arsenate,
zinc sulphide, calcium oxalate, &c., so that the use of acetic acid is
valuable in some separations. The commercial acid is strong enough for
most purposes, and is used without dilution.

~"Aqua Regia"~ is a mixture of 1 part by measure of nitric acid and 3
parts of hydrochloric acid. The acids react forming what is practically
a solution of chlorine.[6] The mixture is best made when wanted, and is