You need to use 70% ethanol for an experiment. You only have a small quantity of 100% ethanol which is not enough to dilute and make the volume of 70% that you need. A chemistry friend of yours says he will make and distill some 70% ethanol for you. Unfortunately, your experiment doesn't work and you suspect the 70% ethanol is to blame. Suggest a way to determine whether the supplied 70% ethanol was the correct proportion of alcohol. I'm thinking you could use specific gravity with pure water as a reference. Is that right? Any suggestions?