In its pure form, it is shock sensitive (i.e. physical shock can cause it to explode), and degrades over time to less stable forms. This makes it highly dangerous to transport or use in its pure form.
The compound follows similar rules to other explosives. An explosion is essentially very fast combustion, and combustion requires fuel and oxidant. This compound, as you can see below, essentially contains both of these components. If you detonate this compound under pressure, it will explode to form thousands of times its original volume in hot gas.
The making of nitroglycerine is obviously very potentially dangerous as there is the hazard of the product exploding. Do not attempt to make this yourself.
The industrial manufacturing process uses a 50:50 mixture of fuming sulphuric acid (fuming means it is very concentrated) and red fuming nitric acid. This produces the nitronium ion in situ, and this attacks the glycerine molecule at the negatively charged oxygen atoms. The functional group NO2 is thus added, adding extra oxygen atoms to the flammable substance glycerine.
The use of strong acids almost always produces an exothermic reaction, and this case is no exception. However, if the mixture becomes too hot, it will explode. Thus, the acid mixture is added slowly to the reaction vessel containing the glycerine. The reaction vessel itself is cooled using ice-cold water, or other coolant mixture at around 0°C. The vessel itself has an emergency trap door at the bottom of it, which hangs over a large pool of very cold water. If sensors in the mixture detect the temperature rising too rapidly, then the whole mixture can be dumped into the ice cold water, which will prevent an explosion if done in time.
Why is it used as a medicine? Another name used commonly in medical context is glyceryl trinitrate because nitroglycerine is a chemical compound of nitric acid and glycerine. It can be clearly seen why is is called trinitrate in this chemical formula :
CH2-NO2 | CH-NO2 | CH2NO2
- chest pain subsides
- blood pressure lowers
- heart beat increases
All in all, to better understand it, one must delve more deeply into blood circulation physiology.