Yesterday, I described how I made some hand sanitizer using the WHO’s recipe. Today, adventures with a Proof and Tralles Hydrometer. Read on for the mixed results.
First, one of note on yesterday’s post. As some of you pointed out, you need to use 3% hydrogen peroxide, not some higher grade stuff – that shit will dissolve your hands, not clean them.
I bought the hydrometer from Amazon for $7. Since the first one didn’t ship on time, I ordered a second one. Both arrived today, of course. This thing is not the world’s most complex or probably accurate instrument, but we’re just looking to make sure that our hand san is in the ballpark of the 75% the WHO recommends for their isopropyl alcohol formula, which is way above the 60% the CDC recommends as the minimum alcohol content.
These things are 11 inches long, and ideally you’d use a graduated cylinder or other tall narrow container for your sample. My kitchen lacks that piece of equipment, and I’m impatient, so I found the biggest, fullest bottle of liquor I have for a rough-and-ready test, some 80 proof (40% alcohol) Brugal Anejo Dominican Rum.
The procedure is to place the hydrometer in the bottle, make sure it isn’t touching the bottom, spin it to get rid of air bubbles, and I found that pushing it in and letting it float up a couple of times would get you to a repeatable reading. This reading is about 39% alcohol. At 68 degrees F, the reading is supposedly ~3% high, according to a correction chart supplied with the hydrometer, so it’s more like 36%. Either Brugal is lying to us when they say their liquor is 40% alcohol, or some alcohol evaporated out, or this thing is a little off. That’s the problem with kitchen chemistry, you can’t fully trust your references. (Both hydrometers read about the same on all samples, by the way.)
The second reference I tried was 70% rubbing alcohol from a bottle I opened two days ago. I used a new Smartwater bottle as the container.
This is around 76%, and with the temperature-based correction factor of 3%, we’re at 72%. The WHO guidance says that a 75% isopropyl solution will read at 77% on this type of instrument (which is made for ethanol), so a further correction factor of ~2% gets us to ~70%, which is what it says on the bottle.
Alright, time for the grand finale. Here’s the hand san.
That’s just a tiny bit above 80, with a correction factor of 3, we’re at ~77%, which the WHO says is what this instrument will read for 75% alcohol, the target for this formulation. So, Yahtzee. This will be ready to use by Tuesday afternoon (after the 72 hour wait). Note that I will let the sample I poured into the Smartwater bottle sit for an additional 72 hours in case I introduced any contaminants.
Final formula for ~5 liters of hand san:
3784 ml 99% Alcohol (8 16 oz bottles)
210 ml 3% Hydrogen Peroxide
73 ml Glycerin USP 1000 ml boiled distilled water
Note that this is ~1.4% glycerin, for those of you who were worried that it would throw off the hydrometer.