Why are a calico strainer and chloroform used in a British Pharmacopoeia assay of milk of magnesia?
Ok I understand where you got chloroform from.

This is not the assay of milk of magnesia, but the extemporaneous preparation.

In extemporaneous preparations chloroform is used as:


a general anaesthetic
a carminative
flavouraing agent
preservative 


So in the case of mik of magnesia it has two main roles that is a carminative and a preservative.

Hope this helps