Hi Rodg,
Ammonium chloride (the hydrochloric acid salt of ammonia) can in theory be used as a source of ammonia for a fishless cycle. However it is mildly acidic so if your water is soft it may cause the pH to drop ( as low as 5 in theory). To calculate how much you will need I am assuming you are 90g uk which is approx 400 litres. 5ppm or 5 mg per litre would require 2g of "pure" ammonia. Ammonium chloride is approx 30 % ammonia so you would need about 6 g of ammonium chloride to get 5ppm. I would play it safe and add it in portions of about 1g at a time, predissolved in some water and test your pH and ammonia levels as you go.
Cheers
Businesslamb
