why yolk of boiled egg turn black from outside after some time?
92973
Actually, the yolk begins to turn greyish when it is over cooked.  Don't cook your eggs for as long, and they will stay perfectly yellow!\n\nI'm in culinary school, and before my teacher told me this, I thought the yolks in hard-boiled eggs were supposed to be grey on the outside because they always are when my mother makes them!
159004
nichrome loops turn dark after repeated heating, but are less expensive.
369550
8 years on a farm and I never saw to chicks hatched from one egg. I did see plenty of double yoked eggs when we cooked them.
547020
Make two holes in the egg, with a needle, one at the top and one at the bottom of it. With a long needle brake the yolk, shake it and blow out the content. Fill the egg shell with the help of a syringe, with epoxy-resin and let it harden. You must fill the holes too and make a smooth surface. Paint the egg and it will look like a real one.
1420
Good question.   Could be a number of reason, but my guess would be that you have some salt in your boiling water.    When NaCl solution is placed in a flame the Na cation gets ionized and yellow light is given off.    It doesn't take much salt for you to see this effect.   You will see this even with regular tap water, since it also has a small amount of salts dissolved in it.    \nIn fact, standard distilled water is usually not pure enough to avoid this effect.    That's why chemist buy special stills to make ultrapure water for experiments.
1095981
Not spoiled, but fresh:\n\n\nBlood Spots\nAlso called meat spots. Occasionally found on an egg yolk. Contrary to popular opinion, these tiny spots do not indicate a fertilized egg. Rather, they are caused by the rupture of a blood vessel on the yolk surface during formation of the egg or by a similar accident in the wall of the oviduct. Less than 1% of all eggs produced have blood spots. \n\nMass candling methods reveal most eggs with blood spots and those eggs are removed but, even with electronic spotters, it is impossible to catch all of them. As an egg ages, the yolk takes up water from the albumen to dilute the blood spot so, in actuality, a blood spot indicates that the egg is fresh. Both chemically and nutritionally, these eggs are fit to eat. The spot can be removed with the tip of a knife, if you wish.\n\nhttp://www.aeb.org/LearnMore/EggFacts.htm
544139
boil it first then put some iodine on it. if it turn blue black it mean that it contain starch
646111
You can turn it black with an iodine solution, then turn it back with sodium thiosulphate solution. Neat trick.
1099287
It's due to the chemical compositon of the egg.  It's like putting a lot of chemicals together and then heating it.  An egg is made of many chemical including carbohydrate,  proteins, minearls, vitamins, lipids, amino acids, etc.  The link below gives a good description of what an egg is made of.  If you were to put all these chemicals together in a beaker and heat it up, you would get the same result.
157272
It very well may be surface only discoloration...buff an area and see.Just because it blued a little is no reason to think it is contaminated deeper. The blueing is oxadation due to the heat.
501228
when air is compressed, it heats up. this could be circulated within the incubator to warm the eggs.
64495
The pressure within a chicken egg may be rather nominal, because eggs breathe without lungs.  Oxygen is free to diffuse through the shell.  Water is nearly incompressible, the effect even seven miles down at the bottom of the sea is nil.  Gas is highly compressible and you have to halve the volume to double the pressure at constant temperature, per the perfect gas laws.\n\nMost boiled eggs are not perfectly ovalic because there is an air space within the shell.  That air space would resist any increase in "hydraulic" pressure and excess gas should diffuse out of the shell.\n\nOf course a spoiled egg may build up pressure due to rapid decomposition and an egg shell would be fairly strong to retain it.  Never microwave eggs because they may build up steam pressure and make a real mess.  Early microwave machines had perforated plastic doors rather than solid glass and I recall one unhappy fellow who received a polkadot egg spattered shirt.  Good luck.
432190
If it is not broken, see if you can get it back into the nest.  If not, wrap it in a dry washcloth or soft paper towel.  You can keep it under a low wattage bulb (like 25 watts) and turn it ever so often.  Just turn it a little at a time every couple hours. (mama bird shifts her eggs around with her beak when she is sitting on them)  The robins have just laid their first batch of eggs for the spring and they will be hatching in a week or two.  The robins hatch 12-14 days after the mom lays her last egg.  If nothing happens in a week or so, hold the egg up to the light...if you can see light through it there is no baby...if it is a solid blue there is a bird in there.  If it still doesn't hatch, you tried!  If it hatches, take it to the local animal shelter and they will handle it from there.  Should you have any questions please contact me!
404922
It may be over-heating
394045
The same amount of time as it would outside of the cupboard.  It's a gas the fruit gives off that causes ripening.
966792
Eggs are prone to the same bacteria as other foods.  Refigeration slows that growth, but doesn't stop it.  Also, egg shells are not made of lead.  They are permiable to oders and other things in the refigerator, just as a piece of meat would be.  All of those icky things can seep into an egg shell just as easily as anything else (think about how dying easter eggs also gives the tint of that color to the inside of the egg).
435869
You can still have eggs without them being fertilized. Chickens or people.You know that little white speck you sometimes see in chicken eggs?(Raw ones)That's an egg that has been fertilized.