To make a 1 to 3 parts mixture, you need 1 part of one substance and 3 parts of the other substance.

For example, if you wanted to make 1 part soap and 3 parts water, you would mix 1 cup of soap and 3 cups of water.

In general, to make a mixture of 1 part of substance A to 3 parts of substance B, use the following formula:

[Substance A] = Total Volume / 4

[Substance B] = (3/4) * Total Volume

Where [Substance A] is the amount needed for substance A, [Substance B] is the amount needed for substance B, and Total Volume is the desired total volume of the mixture.