this is a good Question. For a Chemis, 1:1 means "stock solution", i.e. one part of solution A becomes one Part of solution B. 1:9 means one part Solution A becomes nine parts Solution B. In photography, however, 1:1 sometimes means 1+1. If you do not have an example in a manual, you'll have to make a guess. In your case, 1:9 most probably means 1+9, because it is a more convenient and thus more usual form. In this case take 1/10th of a gallon stock solution and fill it up to one gallon.