Is it correct that the total of the purchase invoices recorded in the purchases book is posted to the debit side of the purchases account in the ledger and credited to the accounts of suppliers?
Yes, purchase is an expense account, therefore, following the rule 'increase in expenses is debited', purchase account is debited. Since, the purchase book contains records of credit purchases, the suppliers' account is credited following the rule applicable to liabilities accounts i.e., 'increase in liabilities is credited.