A collection of random chemistry factoids.
This document is rather loose when refering to % solutions. These can be %V/V, %W/V, etc.

When a solution is X% of something that you would normally obtain in a dry state, that usually means X grams of whatever in 100 mL of solution. For example, a growth medium that is 2% CaCO3 has 2 grams of CaCO3 in 100 mL of that medium.

Likewise, X% of a liquid (e.g. 10% apple juice) means 10 mL of that in 100 mL of the solution. Note that 100 mL is the final volume. To make this you would add 10 mL apple juice to 90 mL of whatever.

A rough guideline for those without good scales is that 5 grams of many powdered chemicals is about 1 teaspoon (5 mL).
DIFCO MRS Broth is: 10 g/L Peptone, 8 g/L Meat extract, 4 g/L Yeast Extract, 20 g/L Glucose, 2 g/L Dipotassium hydrogen phosphate, 5 g/L Sodium acetate trihydrate, 2 g/L Triammonium citrate, 0.2 g/L Magnesium sulfate heptahydrate, 0.05 g/L Manganous sulfate tetrahydrate. This is made up to volume, 0.1% Tween 80 is added, and autoclaved.