Переведите предложения:
1. In experiments with ozone one can take advantage of the fact that essential oils absorb ozone without decomposition.
2. To investigate the properties of oxygen care should be taken to have the gas in pure form
3. Hydrogen sulphide being very poisonous, care should be taken in the laboratory not to inhale it
4. Soluble barium salts being poisonous, care is taken to remove them.