Sulaiman - 31-8-2019 at 03:02
For no particular reason other than boredom I just ordered 25g of Methyl Violet from China via eBay
https://www.ebay.com.my/itm/25g-Methyl-Violet-Powder-Aniline...
EcAAOSwX1JcsbRp
Methyl violet (I now discover) has different names and also has three different compounds,
the Methyl violet that I ordered has CAS# 548-62-9 which according to wikipedia
https://en.wikipedia.org/wiki/Methyl_violet
is Methyl Violet 10B aka Crystal Violet aka Gentian Violet.
The molecular formula on the container is C24H28ClN3 which would make it Methyl Violet 6B Cas# 8004-87-3 according to
the wikipedia article.
I thought that I was buying crystal violet, a useful antibacterial agent,
also useful for staining bacteria etc ... but it may not be.
How can I determine which type of methyl violet I have (when it arrives)
(I heve almost no equipment or reagents at the moment) 
Pumukli - 31-8-2019 at 03:59
Afaik all triphenyl-methane dyes are cytotoxic, so it doesn't really matter which one you will receive. They will kill bacteria and probably stain
cells as well.
As I see these three compounds differ only in one thing: they are either primary, secondary or tertiary amines.
Maybe with sodium nitrite you can differentiate between them.
Primary amine is diazotized and N2 can be released, phenol produced, it would switch into a chinoid form, colour change expected. Secondary makes a
nitrosamine, they are usually colored (blue), the original colour of the compound may change. Tertiary amine should not make any particular reactions,
I'd not expect any colour change.
At least this is my theory. 
Let's see others'!
wg48temp9 - 31-8-2019 at 06:00
Its always a good idea to check the CAS# against the name and the formula and any other information they may have in the ad. Particularly so with
dyes and pigments as they have so many names and frequently not unique ones.
The label on your violet looked identical to my violet. So I checked mine again. Its not the same label as yours and unlike your contradictory label
(pic in the ad) and contradictory description in the ad, mine are consistent with the crystal violet. Of cause what it actually is apart from it being
a violet dye i do not know.
I guess chromatography would distinguish them but of cause you need need known samples of both.
On the +side you can complain and perhaps get what ever it is for free.
Then order it again from a different seller without contradictory descriptions of it. Mine was from d-9845 on ebay UK.
I just checked your seller is on ebay UK too with the same incorrect ad. I am tempted to buy but i will wait to see if you get your money back and if
he then does not correct the ad its fair game.
Sulaiman - 31-8-2019 at 17:11
Since posting above I've been googling a little,
and the more I read the less I know 
It seems to me that the three forms of methyl violet (2B, 6B and 10B) are commonly confused with each other in the literature and even by suppliers,
example ;
https://www.fishersci.com/shop/products/methyl-violet-2b-pur...