dave@lsuc.UUCP (David Sherman) (04/09/86)
I have a kind of silly little question that I've been curious
about for a while. Can someone explain to me the principles
on which dish detergent (and, I suppose, any soap) works?
Let's say I have a big bowl which I used to cook food, and I'm
about to clean it in the kitchen sink. I do one of the following:
1. Squirt in some liquid detergent, then fill it with hot water, using
the vegetable spray that's attached to the sink so I can direct
the streams of water all over the bowl. When the water is directed
at the detergent, lots of soapy bubbles appear and I feel good.
Half an hour later I wipe the thing out.
2. Squirt in some dish detergent, then fill the bowl from the tap.
The soapy bubbles concentrate in the area underneath the tap,
but do cover the whole bowl by the time it's full.
3. Fill it with hot water first, then remember to put in the detergent.
Now, if I do 3, I don't get any of those satisying bubbles. But
it's not the bubbles that make the bowl easy to clean, is it?
Should 3 give me a worse cleaning than 1 or 2? Why? How does soap work?
(Followups directed to net.misc.)
Striving for a deeper understanding of the important things in life,
Dave Sherman
The Law Society of Upper Canada
Toronto
--
{ ihnp4!utzoo pesnta utcs hcr decvax!utcsri } !lsuc!davelarry@kitty.UUCP (04/18/86)
In article <1178@lsuc.UUCP>, dave@lsuc.UUCP (David Sherman) writes: > I have a kind of silly little question that I've been curious > about for a while. Can someone explain to me the principles > on which dish detergent (and, I suppose, any soap) works? > Let's say I have a big bowl which I used to cook food, and I'm > about to clean it in the kitchen sink. I do one of the following: > > 1. Squirt in some liquid detergent, then fill it with hot water, using > the vegetable spray that's attached to the sink so I can direct > the streams of water all over the bowl. When the water is directed > at the detergent, lots of soapy bubbles appear and I feel good. > Half an hour later I wipe the thing out. > 2. Squirt in some dish detergent, then fill the bowl from the tap. > The soapy bubbles concentrate in the area underneath the tap, > but do cover the whole bowl by the time it's full. > 3. Fill it with hot water first, then remember to put in the detergent. > > Now, if I do 3, I don't get any of those satisying bubbles. But > it's not the bubbles that make the bowl easy to clean, is it? > Should 3 give me a worse cleaning than 1 or 2? Why? How does soap work? Well, I suppose I'll jump in and get my feet wet in this discussion. Let's start by describing how soaps and detergents work. A ``surfactant'' (aka surface-active compound) is any substance which lowers the surface tension of water. A type of surfactant is ``soap'', being generally a sodium or potassium ester of a long-chain carboxylic acid. These carboxylic acids can be derived from natural vegetable oils (e.g., palm oil yields palmitic acid) and animal fats (e.g., tallow yields stearic acid). These carboxylic acids are combined with an alkalai (such as sodium hydroxide, better know as lye) whereupon they undergo a process known as saponification to form a soap. This process is the earliest method of making soap, and was known in ancient times. For example, the actual chemical name for a simple soap is sodium stearate. Most "dirt", grease, and other foreign matter which covers an object to be cleaned is organic material which is insoluble in water. Grease which covers say, a metal pot, sticks to the pot by means of the surface tension of the grease (this is sort of over-simplified, but close enough). Placing a greasy pot in plain water does essentially nothing to free the grease from the pot, because the grease is insoluble in the water, and the water has a high surface tension compared to that of the grease. Now enter soap... Sodium stearate (and other soaps) have molecules where ONE END is highly polar (i.e., it is hydrophilic, or soluble in water) and the OTHER END is non-polar (i.e, it is lyophilic, or soluble in say, oil). Soap is soluble in water to the extent that it forms a colloidal solution (rather than a true solution). In fact, soap molecules in water solution form aggregates of such molecules which are called ``micelles''. When grease on a pot comes in contact with water (whose surface tension is now reduced) and the soap micelles, the grease DISPERSES into fine particles which are now ENTRAINED in these micelles. The bottom line of all this is that the grease is NOW IN SOLUTION (held by the micelles), and no longer clings to the pot! Now, getting back to your question about methods 1, 2, and 3... For practical purposes, the presence or absence of soap bubbles means nothing. What is important is mechanical agitation. The dispersion of grease into the soap micelles will occur eventually as a result of Brownian motion. However, it will occur MUCH, much faster with some mechanical agitation as a result of scrubbing or shaking the object to be cleaned. A spray of water against a pan will help with this agitation PROVIDED there is already some soap in contact with the pan; otherwise the effect of the water will be lost execpt for removal of gross deposits of grease. So far I have talked about ``soaps''. Soaps with the chemical composition as mentioned above have an undesireable characteristic: they combine with calcium, magnesium or ferric ions in hard water to form insoluble compounds (e.g., sodium stearate will form calcium stearate) which results in soap ``scum''. To circumvent this problem, a surfactant class called ``detergents'' was developed. An example of a simple detergent is sodium lauryl sulfate; coconut oil undergoes hydrogenolysis to form lauryl alcohol, which is then treated with sulfuric acid to form lauryl hydrogen sulfate, which is then combined with sodium hydroxide to form the sodium lauryl sulfate. Detergents do NOT form insoluble products with metal ions in hard water; therefore, no undesireable soap scum. ALL domestic water is hard; some is just less hard than others (even with a water "softener"). To sum up... ``Soaps'' are not the same as ``detergents'', despite the fact that the terms are used interchangeably by many people; both of these substances are types of ``surfactants''. Surfactants allow otherwise insoluble oils and grease to enter a water solution; this permits cleaning. I won't talk about phosphates in this article... ==> Larry Lippman @ Recognition Research Corp., Clarence, New York ==> UUCP {decvax|dual|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry ==> VOICE 716/688-1231 {rice|shell}!baylor!/ ==> FAX 716/741-9635 {G1, G2, G3 modes} seismo!/ ==> "Have you hugged your cat today?" ihnp4!/
gm@trsvax (04/20/86)
Mr. Bubble responds: When using any kind of detergent in water, there is a certain probability (3-1 on "Big Bopper" to Place in the 6th) that intense chemical and nuclear reactions will take place between the valence electrons in the P-electron shell of the water molecule and the partially unfilled outer electron shell of the detergent molecule. This produces a rapidly spinning vortex, which in some cases, can actually open a time-space portal to another part of the galaxy. Depending upon what part of the galaxy these vortexes (vorTexas?) open to, you can acquire or loose all sorts of matter through them. This is why you will notice that sometimes you can place a pair of socks in a washing machine and only one sock will come out. Or you can place a pair of red socks in, but a white and a red sock come out. The bubbles were invented by detergent manufacturers to "shield" the contents of your sink or washing machine against these portals. The larger the bubble, the better shield it makes. But as the bubble becomes larger, the space inside the bubble that it is protecting also gets larger (volume = pi * r^3), which makes it more and more unstable. This explains the behavior that you noticed in case #3 (no bubbles, but it still gets clean). When you don't have any bubbles, you will have a larger amount of these portals opening up in your sink. Matter and energy is being transported back and forth between various parts of the galaxy. Sometimes it can actually open portals between your sink and the inside of a star, which is where it gets the energy to clean your sink. (God knows you don't have the energy or you wouldn't be using detergent in the first place.) "Massbus" is a trademark of Digital Equipment Corp. "Hasn't Scratched Yet" is a trademark of Ajax Corp. (A Beatrice Company!) "Quarter Pounder" is a trademark of McDonald's Corp. ----------------------------- George Moore (gm@trsvax.UUCP)
CJC@PSUVM.BITNET (04/24/86)
Some kinds of detergents, for example those for automatic dishwashers and
spray-and-suction type carpet cleaners, are specially designed to not
make bubbles; also many laundry detergents were made 'low-sudsing' after
people started complaining about soap-sudsy rivers. The important part
is the chemical action, the bubbles just amuse the customer.