Answers to Queries. 215 
stage to carry the razor. The object to be cut is moved by the 
fine adjustment. 
Rust-Stains.—To remove rust-stains from nickel-plated instru- 
ments, thoroughly grease the instrument, and after several days 
rub with a cloth moistened with ammonia. If any spots are still 
visible, they are touched with dilute hydrochloric acid and imme- 
diately rubbed off. The instruments are then washed and 
polished with polishing powder. 
Preserving Instruments from Rusting.—Immerse them in a 
solution of carbonate of potash for a few minutes, and they will 
not rust for years, not even when exposed to a damp atmosphere. 
To Restore the Polish of Instruments.—Place them in a 
vessel containing a saturated solution of stannous chloride in dis- 
tilled water, and leave over-night. Rinse in running water, 
wiping and rubbing with a chamois to finish. Zinc®chloride gives 
only fair results. 
Etching Liquid for Steel—Mix one ounce of sulphate of 
copper, one-fourth of an ounce of alum, and a halfteaspoonful of 
salt reduced to powder, with one gill of vinegar and twenty drops 
of nitric acid. The liquid may be used either for eating deeply 
into the metal, or for imparting a beautiful frosted appearance to 
the surface, according to the time it is allowed to act. 
Testing Water.—-Heisch’s test for sewage contamination is as 
follows :—Fill a clean pint bottle three-fourths full with the water 
to be tested, and in this dissolve half-a-teaspoonful of the purest 
sugar; cork the bottle and set it in a warm place for two days. 
If in twenty-four to forty-eight hours the water becomes cloudy or 
milky, it is unfit for use. If it remains perfectly clear, it is pro- 
bably safe to use. Another method is worthy of trial:—Half fill 
a bottle with water, cork tight, and set it for a few hours in a 
warm place. Shake up the water, remove the cork, and critically 
smell the air contained in the bottle. If it has any smell (particu- 
larly if its odour is repulsive), the water should not be used for 
domestic purposes. By heating the water, an odour is involved 
that would otherwise not appear. 
Answers to Queries. 
404.—Soda-Lye.—Is a solution of an alkali; water impregnated 
with alkaline salt, imbedded from the ashes of wood. Used in 
soap-making, in neutralising an acid, and in cleansing grease from 
objects, such as thin iron plates in the operation of tinning, etc. 
Viable: 
