Determining Alcohol Percentage
The phenomenon of miscibility is key to drying wood by alcohol soaking. Miscible liquids will reach a uniform concentration when combined in a container. An example is a bottle of wine which maintains a uniform consistency of alcohol and water no matter how long it sets undisturbed.
When a piece of wood is placed in an alcohol solution the phenomenon of miscibility will cause the water in the wood and the alcohol in the solution to migrate until they reach equilibrium. The final alcohol concentration in the wood will always be less than the starting alcohol concentration of the soaking solution.
Replacing water in wood with alcohol is the key mechanism for drying wood faster. Alcohol readily moves through cell walls and has a lower vapor pressure than water. As the concentration of alcohol in the wood goes down the drying time increases. Therefore, it is useful to know the alcohol concentration of the soaking solution.
A hydrometer is one way to measure alcohol concentration. To be more accurate the temperature of the solution needs to be measured to correct for density changes due to temperature. The easiest way to measure temperature is to use a hydrometer with an integrated thermometer. Hydrometers are expensive and breakable. Since a scale is needed to track the drying of wood pieces a method of determining alcohol concentration by weight would utilize existing equipment and minimize cost.
Knowing that alcohol and water have different densities I concluded that the alcohol concentration of a solution could be calculated by a ratio of weights. I contacted Professor Shawn Bearden in Pocatello, ID and ask him if he could help me devise a procedure. Shawn developed the graph and table used in this procedure.
The procedure requires the following:
A scale capable of measuring a minimum of 1 gram(g) increments.
A see through container with a narrow neck to increase the accuracy of the sample size to be weighed.
A copy of the Alcohol Percentage Graph and Table
2. Draw a line about an inch below the top of the sample container. The line needs to be narrow enough to accurately measure each sample.
3. Weigh the empty container and record the weight.
4. Fill the container to the line with water.
5. Weigh the sample and record the weigh.
6. Empty the container and fill it with soaking solution to the measuring line.
7. Weigh the sample and record the weight.
Calculating the weight ratio.
The ratio is calculated by dividing weight of the water by weight of the solution. To be more accurate subtract the weight of the empty bottle from water and solution weights.
609g /527g = 1.155597
The resulting quotient is the ratio and will be a number greater than 1.
Rounded to 4 dismal places, ratio = 1.1556
Converting the quotient to percentage of alcohol concentration.
Using the graph find the ratio on the horizontal or X axis. Read the alcohol concentration on the vertical or Y axis.
Using the table find the ratio and the corresponding alcohol concentration.
After calculating the ratio round the number to 4 dismal places. The first two decimals correspond to the numbers on the chart and graph. The third and forth decimals are used to interpolate the concentration between the values given.
The first 3 numbers of the example ratio 1.15 correspond to the number on the chart for 62.20% alcohol concentration. The next higher ratio is 1.16 which corresponds to 65.79% alcohol concentration.
The last two numbers are used to interpolate between the ratios 1.15 and 1.16. Treat the last two numbers as a percentage of the value between 62.2 and 65.79. In the example the last two numbers become 56% (0.56) of the difference between 65.79 and 62.20.
65.79 - 62.20 = 3.59
3.59 x .56 = 2.01
62.2 + 2.01 = 64.21
Add the difference to the lower number which yields the alcohol concentration.
For alcohol soaking purpose it is not necessary to do the math to determine an exact percentage of alcohol concentration. A ballpark number is good enough.
Experience has shown that higher concentrations of alcohol in the soaking solution will produce the best results of faster drying times with less degradation of the piece. Therefore it is recommended that the starting alcohol concentration be greater than 60%.
Wood can be successfully dried with lower concentrations but the advantages of soaking in alcohol are diminished. Drying time will increase. Because there is more water in the wood, which does not migrate out of the wood as easily as alcohol, more stress will develop across the walls of a piece which increases the probability of cracking.
It is only necessary to weigh the water once as long as the same bottle is used for weighing the solution sample. The water weight for the bottle used in the example will always be 609g. For subsequent test it will only be necessary to weigh a solution sample.
After weighing the solution rinse out the bottle with a small amount of alcohol and add it to the solution container. Compressed air blown into the inverted bottle will insure it is dry.
Alcohol Percentage Graph and Table is available in PDF format. Print a copy of the chart for your convenience.