Exposure Meter

(See Actinometer.) Methylated Alcohol.

(See Alcohol.) Methylated Spirit

(See Alcohol.)

Metol

(C6H3 [OH] CH3 NACHS)2 H2SO4.

Monomethylpara-amidometacresol Sulphate. White powder. Soluble in water. Use: An energetic reducing or developing agent. Produces negatives of gray softness. An excellently balanced developer is one of a combination of metol and hydroquinon. (See Hydroquinon.) The combined developers work equally well for both plates and bromide or developing papers. Metol is poisonous to some people, causing very disagreeable and irritating sores on the hands.

Metol-Quinol

A name given to the combined developer composed of metol and hydroquinon.

Metric System

A system adopted by the French government in 1879. It is now, practically, universally used in all scientific work. The METER is a unit of length.

The ARE is the unit of surface, being the square of the meter. The LITRE is the unit of capacity and is the cube of a tenth part of the meter.

The GRAMME is the unit of weight and is equal to the weight of the cube of a hundredth part of a meter of distilled water. Each unit has its decimal multiples and sub-multiples - i. e., weights and measures ten times larger, or ten times smaller, than the principal units. The derivation of the prefixes denoting the multiples are from the Greek; those denoting sub-multiples are taken from the Latin.

Microphotography

(See Photo-micrography.)

Use of Microscope

Middle-Angle Lens. (See Angle, Normal.)

Middle Distance

(See Distance, Middle.)

Reversing Mirror

A plain mirror set at an angle of 45 degrees and placed close to the lens. The image is reversed by photographing it as it appears in the mirror. The mirror must be constructed so reflection comes from the top surface, in order to do away with a double image; therefore, an ordinary looking-glass will not answer the purpose.

Silvering Mirror

Silver Nitrate (Coarsely powdered) ..............

1/2 oz.

Liquid Ammonia...........................................

1/4 oz.

Water.............................................................

1 1/4 ozs.

Mix and allow to stand for 24 hours, then filter and add,

Naphtha...........................

after which add,

30 ozs.

Oil of Acacia.............................

25 drops.

After allowing to stand for another six hours the solution is ready for use. Clean the glass to be silvered and give it a highly polished surface; then place in a horizontal position and build a wall of putty or similar material around the edge, so it will be possible to have the solution on the glass at a depth of 1/8 to 1/4 of an inch. Now, prepare a solution of

Oil of Cloves.............................

1/2 oz.

Spirits of Wine..........................

1 1/2 ozs.

Drop from 6 to 12 drops of this mixture into the silver solution at different places. The more oil of cloves used the more rapid will be the deposit of the silver. The operation, however, should occupy a couple of hours. The following formula, known as Martin's method for silvering glass, is one that may be employed when it is desired to re-silver mirrors or reflectors. Mix each solution separately:

(a)

Nitrate of Silver....................

175 grs.

Distilled Water ......................................

10 ozs.

(b)

Ammonium Nitrate...............

262 ozs

Distilled Water.....................

(c)

Caustic Potash (pure).............

437 1/2 grs.

Distilled Water ......................................

10 ozs.

(d)

Sugar CAndy (pure)................

219 grs.

Distilled Water..............

5 ozs.

Dissolve and add,

Tartaric Acid................

. 50 grs.

Boil in a flask for ten minutes, and when cool add,

Alcohol..................... 1 oz..

Distilled Water to Make.............

10 ozs.

When ready to use mix equal parts of a and b, also mix equal parts of c and d; then add the two solutions in the dish in which it is intended to silver the glass. Suspend the glass face downward.