public void adjustAir()
	{
		int currentAir = 0;					// current number of air molecules
		for(Molecule mole : getMolecules())
			if(mole instanceof Air)
				currentAir++;
		
		int desiredAir = (int)(pres/100);	// desired number of air molecules
		
		if(desiredAir > currentAir)			// not enough air
		{
			for(int i = currentAir; i <= desiredAir; i++)
				addAir();
		}
		else if(desiredAir < currentAir)	// too much air
		{
			for(Molecule mole : getMolecules())
			{
				if(mole instanceof Air)
				{
					molecules.remove(mole);		// remove air
					currentAir--;
				}
				
				if(currentAir == desiredAir)	// until desired amount is reached
					break;
			}
		}
	}