Finding methanol purity by density

IMPORTANT: Any methanol purity tests you do will be highly temperature dependent. Be sure to measure the sample temperature first.

1. You can use a calibrated methyl alcohol hygrometer, but you will need to ensure your sample is at the same temperature at which the hygrometer was calibrated.

2. (my preferred method) You can use a calibrated 1 litre measuring flask, and accurately measure the weight of 1 litre of sample methanol at known temperature.

Assuming water is the pollutant, this table gives you the relationship between density and purity ....

Methyl Alcohol (CH3OH) Density kg/litre

% 0 DegC 10 DegC 15 Deg C 20 DegC
75 0.8754 0.8676 0.8629 0.8592
76 0.8729 0.8651 0.8604 0.8567
77 0.8705 0.8626 0.8579 0.8542
78 0.868 0.8602 0.8554 0.8518
79 0.8657 0.8577 0.8529 0.8494
80 0.8634 0.8551 0.8503 0.8469
81 0.861 0.8527 0.8478 0.8446
82 0.8585 0.8501 0.8452 0.842
83 0.856 0.8475 0.8426 0.8394
84 0.8535 0.8449 0.84 0.8366
85 0.851 0.8422 0.8374 0.834
86 0.8483 0.8394 0.8347 0.8314
87 0.8456 0.8367 0.832 0.8286
88 0.8428 0.834 0.8294 0.8258
89 0.84 0.8314 0.8267 0.823
90 0.8374 0.8287 0.8239 0.8202
91 0.8347 0.8261 0.8212 0.8174
92 0.832 0.8234 0.8185 0.8146
93 0.8293 0.8208 0.8157 0.8118
94 0.8266 0.818 0.8129 0.809
95 0.824 0.8152 0.8101 0.8062
96 0.8212 0.8124 0.8073 0.8034
97 0.8186 0.8096 0.8045 0.8005
98 0.8158 0.8068 0.8016 0.7976
99 0.813 0.804 0.7987 0.7948
100 0.8102 0.8009 0.7959 0.7917
% 0 DegC 10 DegC 15 Deg C 20 DegC

So, as long as 1 litre weighs less than 800g at 20C, it should be OK to use directly. (Better than 97% pure)