Sentence:  [...] it was not unfrequent for a good bargain to be struck with him by one or more of the public functionaries, the difference between the sum proposed and accepted being settled against the interests of Mynheer Krause, by the party putting him in possession of some government movement which hitherto been kept <WSD>"in petto</WSD>". 
Meaning of the word marked with <WSD> tags:  Secret, private.