• Blog Stats

    • 72,568 hits
  • Archives

  • Enter your email address to subscribe to this blog and receive notifications of new posts by email.

    Join 148 other followers

  • Copyright notice

    This blog entry and all other text on this blog is copyrighted, you are free to read it, discuss it with friends, co-workers and anyone else who will pay attention.

    If you want to cite this blog article or quote from it in a not for profit website or blog then please feel free to do so as long as you provide a link back to this blog article.

    If as a school teacher or university teacher you wish to use content from my blog for the education of students then you may do so as long as the teaching materials produced from my blogged writings are not distributed for profit to others. Also at University level I ask that you provide a link to my blog to the students.

    If you want to quote from this blog in an academic paper published in an academic journal then please contact me before you submit your paper to enable us to discuss the matter.

    If you wish to reuse my text in a way where you will be making a profit (however small) please contact me before you do so, and we can discuss the licensing of the content.

    If you want to contact me then please do so by e-mailing me at Chalmers University of Technology, I am quite easy to find there as I am the only person with the surname “foreman” working at Chalmers. An alternative method of contacting me is to leave a comment on a blog article. If you do not know which one to comment on then just pick one at random, please include your email in the comment so I can contact you.

Nitrous oxide no laughing matter !

Recently I wanted to try an experiment, while some of you will know that oxygen will relight a glowing splint some other gases will also relight the glowing splint. As a teenager I had once used a wash basin and a half pint glass to collect the nitrous oxide left in a can of squirt cream which is left after the last of the cream has been used.

I was able to relight a glowing splint with the nitrous oxide.

I choose twenty years later to repeat this experiment, this time I used this time a highly scientific gas collection system. A bucket of water and a glass jar.

I collected the gas the same way as before, this time when I jabbed the glowing splint in the jar nothing happened. I then did what a good scientist does and I looked at my equipment and considered my experimental technique. The technique seemed OK, I repeated the test using pure oxygen gas (surprise surprise it worked) and then I looked at my reagents. The wooden coffee stirrer was shown to work OK with pure oxygen so I looked at the squirt cream.

I saw that the brand of squirt cream I had used employed a blend of nitrous oxide and nitrogen. So the nitrous oxide was too dilute for the experiment to work. I then considered the matter, as nitrous oxide is much more lipophilic than nitrogen the gas in the can would have been more nitrogen rich after I finished off the cream (or more nitrous oxide lean) than it was when I bought the can.

Rather than cursing the fact the experiment failed, I started to think about what do we learn for a failed experiment. To me an important part of science is testing hypothesis, here is I had tested the hypothesis that

Mark Foreman can use the gas in squirt cream cans to relight glowing splints

I had found that I had shown this hypothesis to be wrong. A new hypothesis was needed (I will get back to it later). I thought long and hard about the experiment and science. Karl Popper wrote years ago about the problem of scientific thought, he came up with the idea that “no theory is right it is at best not wrong yet”. His thoughts were a reaction to some people who would twist everything to fit their pet theory.

Popper thought it was better to create a hypothesis and then subject it to a series of tests which have a reasonable chance of proving the hypothesis is wrong. This is a good idea and a great step forward from induction.

Induction is a dangerous system of thinking, it is not self correcting. An error can infect an entire subject. The inductive method (at its worst) works like this.

1. I saw a woman walking past my house.

2. She wore pinks shoes and was walking a westie dog.

So from these two statements you would come up with the very stupid statement that

“All women wear pink shoes and walk everywhere with a westie dog”

It is better to form a hypothesis that

“All women wear pink shoes and when they walk anywhere they go with a westie”

A quick observation of the women of my town indicates that most of them do not have a westie. So the hypothesis is clearly wrong ! But then I thought what one of the  university teachers (Ed Smith) who taught me said to me once. He told me that in synthesis work that a failed experiment proves very little, the synthesis can fail for many reasons. perhaps you heated it too much or too little, maybe you mixed the reagents wrongly, perhaps one of the reagents was defective or perhaps your lack of skill made it impossible for you to make the chemical product. So he was saying that only a positive result is of use.

This brings us to a problem, how do we do chemistry in such a way that we can keep both Ed and Karl happy. I would say that hope exists. We can do it by having control, blank or background samples in the experiment. We need to compare the thing which expect to work in a positive way with a sample which lacks substance X which our chemical theory suggests will make something happen. Then we can keep Karl happy. To deal with the point which Ed Smith raised we need some control samples which contain substance Y which we already know works and thus allows us to test our experimental method.

One of the things which is important to note in science is that science should be repeatable. It should be possible to make the same experiment work again and again so that we can tell it was not a freak result. The squirt cream can had an unexpected effect. I tend to give my dogs a little squirt cream (they love it), I soon noticed that they come running to the kitchen each time they hear the sound of either the protective lid being taken off the can or cream being squirted out. Thus I have conditioned my dogs in a Pavlovian manner. While my repeating of Pavlov’s experiment is not a major discovery in science, it is still an observation which confirms Pavlov’s work. I can test his hypothesis by opening the squirt cream can and not giving any to the dogs. This cruel experiment allows me to test the hypothesis rather than just using induction.

I have a new squirt cream can in the fridge, I bought a different brand. The label suggests that the propellant is pure nitrous oxide. When I finish off the cream I will do the experiment again and I hope to then post the film here.

Disclaimer, while Dr Mark Foreman takes all reasonable care to comment on interesting chemistry and create safe and enjoyable experiments I accept no responsibility for any death, injury, disease, property damage, prosecution, criminal court case, tort, civil court case or other adverse outcome resulting from you trying out an experiment of mine or using any information I provide. All experiments are done at your own risk. If you are not an adult you must consult your parents and/or science teacher before trying an experiment. If you are doubt about your ability to do the experiment in a safe manner then do not attempt it. Also I accept no responsibility if your mum/dad/teacher/policeman/(insert some other authority figure) tells you off for doing the experiment. Also I am not responsible for your moral, social and spiritual wellbeing. Also if you hate the experiment and do not enjoy it or are left with an intense feeling of self disgust then again I am not responsible. If you read this disclaimer or anything else I write and have some adverse reaction to my words such as going insane, laughing yourself to death, pushing your blood pressure through the roof or some other effect then again I accept no responsibility. Also if you use information in my blog to answer an exam question then I offer no warranty to how good the information is. If you take material from my blog and try to pass it off as your own when you hand in your home work then I take no responsibility for you or offer any sympathy when your teacher tells you off (I hope that the teacher is reading this blog also)

Advertisements

Go on, Have your say !

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: