As we discussed in a previous post, liquid nitrogen is not only difficult to order online, but also has some unbelievably cool science behind it. We discussed how the cooling effect of liquid nitrogen is due to its very low boiling point (−196 °C), and for this reason it can quickly freeze human skin upon contact. This application is referred to in the scientific community as ‘cryotherapy’. The origin of the term comes from the Greek words for ‘cold’ and ‘cure’, and is essentially the use of low temperatures to help heal or cure certain conditions, such as removing benign lesions from the surface of the skin or preserving live tissue. As one can imagine, this means that cryotherapy likely has many applications, but today we will specifically discuss the use of liquid nitrogen sprayers in removing lesions and freezing tissue.
When was the last time you had to roll up your sleeves, soap up a rag, and wash a nice sink-load of dirty dishes? I’m guessing last night, unless you’re a bachelor. In that case, it’s better if you don’t answer. Well, in the 1950s folks got pretty sick of washing dishes and laboratory equipment the same old way it had always been done. And no, I’m not referring to the advent of the automatic dishwasher. I’m referring to ultrasonic cleaners! Although they didn’t see home use until around the 1970s, ultrasonic cleaning was used extensively in industrial application after its discovery. Utilizing sound waves, the device emits variable, oscillating frequencies of ultrasonic waves into fluid within a container. By emitting the sound waves into liquid, they can travel throughout the container and disperse their energy to any particles submerged within. In the case of a dirty beaker, these sonic waves will bounce off of the beaker and the contaminants on top of it, effectively loosening and removing them in the process. This is thanks to a phenomenon known as ‘cavitation’, in which the ultrasonic waves exert pressure within the liquid and create bubbles, or voids, transferring their force onto any contaminants they come into contact with. Through this action, ultrasonic waves ‘clean’ the contents of the device.
Mixing two things together is pretty easy, right? Well, in most cases it is—the difficult part is separating the components out of a mixture. As dairy farmers of the 19th century discovered, there had to be a better way to quickly separate the cream from milk without having to wait for the cream to slowly rise to the top. This was not only time consuming, but it also risked having the entire batch of milk turn sour before the cream could be skimmed away. To solve this problem, the first and most primitive centrifuges were created. These early versions of the centrifuge were hand cranked and essentially spun a container around a central pivot point at high speeds, applying centrifugal force to the contents and causing them to separate based on density. This is called the principle of sedimentation. Thus, the denser material would end up on the bottom of the container and the lighter, less dense material would form a surface layer. In the case of milk, the much-desired and valuable cream would rise to the surface for collection.
As far back as the Egyptians (and probably much earlier), civilizations have always needed to compare quantities of goods when trading commodities. One of the earliest records of this surrounds the trade of salt. Specifically, ancient civilizations relied upon displacement of water to calculate volumes of salt being traded. By submerging the commodity in water, they could note exactly how far it caused the water level to rise. Next, once they had estimated the difference in the two water levels, they could approximate the volume of the commodity. However, if there is one thing we know about salt, it’s that it doesn’t handle being submerged in water very well. To circumvent this obvious issue, balances were invented. Although this technology did not initially allow for the calculation of an object’s absolute weight, it did allow for traders to compare the relative weight of two goods. Eventually, this evolved to the point where standard weights and measures could be placed on one side of the scale, to estimate absolute weight, and now to current-day technology that affords us extreme precision and accuracy when measuring weights via advances in digital technology.