OK, Science experts... We are competing in his first ever Science Fair. He is actually in a class to research and time manage this project. It is the early stages, and here is the question. His objective is to prove or disprove the theory that putting silver in milk prolongs its freshness. His submission was good, but the teacher says before he can proceed, what he needs to identify is this: He needs to be able to measure something. We are kind of stuck here as to a scientific way to do that. (We may say the milk is sour but it may be OK to another, etc.) We have the other background plans, but that is what we are stuck on. We looked at Carolina Biological for some sort of bacteria test strip, but can't really find that. Does anyone have a specific suggestion? I would sooo sppreciate being able to move forward with this! Miller
Can you measure the time until it begins to visually turn bad? I know it would be WAY past the drinking point by then, but you would have a definite cue then. Curds, etc.
You will have to culture and grow colonies on plates. One from each milk bottle. You will have to buy a standard growth agar because I don't see the specific growth medium for lactococci and lactobacilli anywhere (most common bacteria in milk becasue of the lactose). He will have to do quite a bit of research about microbiology if he wants to make this work and you will have to make some sort of home made incubator and buy some other supplies. Personally I wouldn't try to identify any of the colonies (unless he is in high school, then they might expect him to know that) but I would just count the colonies and try to demonstrate that there were less, more, or no change. Try here: http://www.hometrainingtools.com/catalog/life-science-biology/cat_agar-petri-dishes.html http://www.hometrainingtools.com/catalog/life-science-biology/cat_microscopic-life.html
We had the same problem - not a real "measurable results" type science project, but it was something ds was really interested in, so our ES said just do it our way. He got honorable mention . . . You could chart the days on how long regular milk goes bad and compare it to the numbers on how long it takes the altered milk to go bad. Maybe also do a "sitting out" vs "in the fridge" version too. Good luck!
Have you tried the Society for Amateur Scientists? They help with science fair projects and have a sort of club they call LabRats. You can Google it because I'm not allowed to put in links.
I must confess that it's seems a rather odd project, but a few things do come to mind: 1) Rule out all other factors. When trying to prove cause and effect, it's very important to remove all other possible causes. For example, you can't use two different gallons of milk because one could be more fresh than the other. You can't run one test on one date and a second test a week later - because different temperatures and air pressures etc. could prove to be a factor. In other words, all experiments should use milk from the same source and must be run in parallel over the same time period. 2) Define the criteria for fresh versus not fresh. Most definitions are going to be rather vague and you need precision to measure an effect. I'd suggest running several tests in advance to see what measurement works best. For example, "sourness" in milk comes from increased levels of lactic acid (I believe), so can you measure the acidity of milk at regular intervals? Maybe something as simple as litmus paper could do this - and I'm sure there are simple gardening kits that allow you to measure pH. By running a few tests, you may find that the pH of the milk does change over time, and then you can define a given pH level as your measure of "no longer fresh". 3) Define what is meant by "silver". What will be the source? Can you measure the exact amount of silver (and its surface area) added to a quantity of milk? 4) Now all the elements are in place and you can run the experiment. For example: - Use 5 identical cups and pour exactly the same amount of milk into each one. - To the first add no silver. Add different amounts of silver to the other four being careful to measure just how much is added. - Keep all five cups together so they all encounter the same conditions. - Measure the pH in each cup at regular intervals (e.g., every hour). - Note carefully when the milk in each cup turns sour (according to the definition you defined earlier). - Examine the results. Is there a correlation between the amount of silver added and when the milk turns sour? - Don't rely on a single experiment. Run it a few times to confirm the results. OK - I made all this up. I have no idea whether the pH of milk changes over time, so that needs checking. If it doesn't, you'll need a different definition of what is sour. But hopefully you can see the method I'm getting at.
Bacteria produce carbon dioxide as a byproduct of their metabolism. Carbon dioxide in water creates carbonic acid. A common experiment uses methylene blue (an acid-base indicator) to track yeast metabolism. You can even use red cabbage extract for that purpose if you calibrate it first. Yes, sour milk really does get "sour." The pH drops once the bacteria really get going. All you really require is some reproducible means to find then the pH goes below some value that's not too far from the starting point. Here's some more information. It's copyrighted material, but I wrote it -- so it should be ok to post it here. The table doesn't copy-and-paste well, but you get the idea. This is from a buffers lab. This procedure contains strong cautions against using the materials at the extreme end (washing soda, for example) without adult supervision and safety equipment. If you did the indicators wet lab, then you already know the color of your indicator for various pH values. This home-made indicator does not last long. Make a fresh batch unless you have some really recently made. If you don't know the colors for different pH values of your indicators, test standard household materials with it. You can use substances such as ammonia, cream of tartar, and so on. Here's a table that may help you. Substance pH limes 1.8-2.0 lemon juice 2.2-2.4 vinegar 2.2 apple juice 2.9-3.3 cream of tartar 3.6 human saliva 6.3-6.6 baking soda 8.3 borax 9.2 milk of magnesia 10.5 ammonia 11.0 washing soda 11.0 lime water 12.0 You'll be adding your "strong" acid and "strong" base to wells (or other small containers if you don't have a well plate) with your buffer solution in them. Definitely use plain water in four of the wells. In pairs of wells, put 6 drops of each solution to be tested (buffer or water or whatever you/ve chosen.) Six solutions would require one-half of a 24-well reaction plate. Put one drop of your red cabbage indicator into each well being used. I have a really nice picture, but can't seem to be able to copy and paste it here.
Now see, I'm no science buff, but I was going to say, there has to be some way to measure the acidity levels as the milk begins to sour! Just need our smarty-pants guy's here to tell you HOW >
I would write the dairy council I would also use the camparison (picturs or journal) of days....... milk with and with out the silver in it........ how long it is safe to drink (measuremen........... in days)
also HOW MUCH silver does it take? are you putting it in a silver pitcher, using a silver stir stick??
