(45) A. L. B. says: 1. I understand that, in modern chemistry, the acids and alkalies are the two extremes of a class of substances called hydrates, the only difference being the radical. In the reaction of nitric acid, HO NO2 or HNO3 on potassic hydrate, KOH is KO NO2 or KNO3, and H2O. Which molecule loses the oxygen atom, and why should one part with it more than the other?
| A. | HNO3 | + | KOH | = | KNO3 | + | H2O |
| Nitric acid | potassic hydrate | potassic nitrate | water |
In this reaction the potassium is considered, by virtue of its greater affinity, as replacing the hydrogen atom in the hydric nitrate; the hydrogen in turn satisfying the OH group to form water. These hydrates are similar only in point of constitution. Their chemical deportments are widely different. 2. What are oxides in modern chemistry? A. The bodies formed by the direct combination of oxygen with the elementary bodies are called oxides. With water some of these oxides form hydrates, as
| K2O | + | H2O | = | 2(KHO) | |
| potassium oxide | water | potassic hydrate |
(46) J. R. M. asks: To have a circular saw run well, should the mandrel have a little end play if it is desired to relieve the saw and guides of strain? A. If the saw is not true or the carriage runs crooked, end play of the mandrel to the extent of the deviations will relieve the strain upon the saw. But if the carriage runs true and the saw true, the mandrel should have no end play.
Minerals, etc.—Specimens have been received from the following correspondents, and examined, with the result stated:
M. S. M.—It is a quartz crystal, the opposite sides of which have been ground flat, probably by artificial means.—F. B.—It is graphite.
COMMUNICATIONS RECEIVED.
The Editor of the Scientific American acknowledges, with much pleasure, the receipt of original papers and contributions upon the following subjects: