How to distinguish the pure silicone oil and ungraded silicone oil?

(1)  Check by your observation: pure silicone oil is a transparent liquid without any smell, but ungraded silicone oil smells bad and in a turbid liquid form.
(2)  To test it by fire. take the pontil or glass rod to dip some liquid , if it can be lighted and fumed when burning, so the liquid is the ungraded silicone oil ,which is a kind of petrochemicals. And, Pure silicone oil can not be fired, which is colorless, odorless, clear, nontoxic. The burning point of pure silicone oil is 320C,but ungraded silicone oil is 100C.
(3)  Freezing point Method: Take 100g of two kinds of silicone oil into refrigerator at the same time. Under temperature of-5 to -10 C for 2 hours, ungraded silicone oil will turn to turbid or frozen ,while pure silicone oil is still clear and transparent as before, and it will not freeze until -5 0 0C.