Liquid nitrogen is very cold. It has a boiling point of -196 Celsius. At that temperature it changes from a liquid to a vapor. So if you have a cup of nitrogen sitting at room teperature, it is boiling. That is why it bubbles and foams. When you stick a grape into the cup of liquid nitrogen, the water within the grape freezes quickly. The same happens with many other objects. When some objects are frozen, they become brittle. You can shatter a frozen grape with a hammer.

Liquid nitrogen is extremely cold and has a boiling point of -196C. Anything immersed in liquid nitrogen freezes very quickly, including items that we are unfamiliar with handling in a frozen state. It is not the liquid nitrogen that makes the materials brittle, it is the extreme cold. (A similar effect can be obtained using dry ice and acetone.) Some materials are naturally brittle in their solid state (i.e., 'frozen'), because of their internal structure. We don't normally think of a sheet of (brittle) glass as 'frozen' in the way we think of water becoming ice, but the change in state from liquid to solid is a freezing process. Any object that contains appreciable amounts of water will become brittle when their water content freezes. This is the reason why frozen fruit can shatter when struck with a hammer: it is mostly ice, which is brittle. Some materials contain compounds that are pliable at room temperature, but harden and become brittle as the temperature falls. Many synthetic materials used in commercial products contain plasticizers or are made from polymers whose properties change when exposed to extreme cold. These temperatures lie outside the normal working range of use of these products, approximately -50C to +50C or higher. Many plastics are quite brittle long before they reach -50C, let alone the -196C of liquid nitrogen. Other materials, including those that one would not normally consider brittle, may go through a phase change at lower temperatures that makes them brittle. This process is called low temperature embrittlement. It occurs in a number of metals with particular atomic structures, of which iron and iron alloys (e.g., various steels) are the most common. One unfortunate example of this was a grade of steel used in shipbuilding for a brief period in the early 20th century. It was discovered that it would become brittle at low temperatures (-10 to -20C), but only after a couple of ships broke up and sank in such weather conditions. ------------------------------------------------------------ Re: "Glass is not solid. It is an extremely viscous liquid" I realize that, but it was used as an example of a very brittle material commonly found around the home. Those lovely ripples in very old glass were much less visible when the glass was first drawn, a manufacturing process rarely used today. ------------------------------------------------------------ Re: "Text Book answer. Not original" Sorry mate, I write all of my answers from scratch. The only thing I had to look up for this answer was the boiling point of liquid nitrogen. If I use material from another source, I always cite the author and place any borrowed text in quotations. I have authored or co-authored over 60 technical reports and papers during my career in engineering R&D and I answer technical questions in a technical manner.

There is a difference between a material "freezing" and a material becoming "brittle" and shattering although they tend to be used interchangeably. Freezing is actually a physical change in the structure or phase of a material such as water which can be a gas, a liquid or a solid. Often, the solid form of a multi-phase material is brittle. Therefore, one effect liquid nitrogen has because of its cold temperature at atmospheric pressure (about -200 F) is to freeze the water in an object, like a rose, thus making it “brittle”. However, in the case of the rose, much more is happening. For example, the water in a rose is stored inside of the plant's cells. When water freezes, it expands and in this case destroys the cellular structure of the plant. Thus, even if you were to thaw a rose after freezing it in liquid nitrogen, it would never be the same again. Additionally, because of the extremely cold temperature of liquid nitrogen, the atomic structure of the plant cells changes thus weakening their ability to hold together. To explain this, you need to understand the concept of "absolute zero" or the temperature at which (theoretically) all atomic motion stops (approx. -460 F). The term theoretical is used because quantum physics does not allow all motion in an atomic system to stop. And, although absolute zero is a construct, laboratory testing does show that atomic motion slows substantially as energy is extracted from a material--i.e., the temperature of the material is lowered. Therefore, as some materials get colder and the atoms within them begin to slow down, the amount of energy holding the atoms together within the material lessons resulting in a weakening of the atomic structure of the material. Think of it as taking the links out of a tinker toy. The colder the material gets, the less links you have until eventually you end up with a very brittle structure or, theoretically, a very fine powder. In summary, brittleness is a phenomenon that can result from lowering the temperature of some materials either through freezing (phase change) or by slowing of the atomic motion.