How to determine which salt is used to hash a password in ruby?

Question

ruby

Good afternoon.
I have an application written in ruby. Now the task is to convert it to Java. And in the current application, user information is stored with password hashing.

class User < ActiveRecord::Base
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable
...
end

I have access to the source and the database, and I know exactly the passwords of several users. Is there a way to find out what "salt" was used to hash the passwords?