Hello and Welcome!

Great question and glad you asked. :)

I have several old books that have the metric system. It is a little complicated at first, but it makes some sense. Compounds are written out in Troy grains, cubic centimeter (milliliter) as being equal fractions to minims or fluid drachm. The Troy symbol looks like an enlarged odd-looking number 3. When you read some of those old formulas the references below will help give you a better perspective.

Below are excerpts from Materia Medica & Therapeutics Dr. Potter published 1917:

"A milligramme as equal to the 1/65 of a Troy grain, a gramme as equal to 15 Troy grains, and a cubic centimeter (or milliliter) as being equal to 15 minims or 1/4 of a fluid drachm.

"Measures may be entirely discarded and fluid quantities expressed in grammes. The average drop of water may be taken as equal to 0.05 c.c [cubic centimeter], the teaspoonful to 5 c.c, the tablespoonful to 20 c.c., the Troy to 30 c.c (or grammes).... (The new U.S.P. substitutes milliliter for cubic centimeter.)


Below is an online conversion table of Metric to English.

http://chestofbooks.com/reference/Henley-s-20th-Century-Formulas-Recipes-Proc...



If you look at the conversion table you'll note that 30-40 cc is a little over an ounce. I hope that helps.