" ...dilute a solvent X in distilled water in a 1:6 ratio" sentence itself is confusing to me. Does that mean dilution ratio or solvent ratio? I always see ratio as, according to Wikipedia, "a relationship between two numbers indicating how many times the first number contains the second.". Which means, in order to have 6 unit of water in the mixture  you need add 6 unit of water in 1 unit of the solvent X (i.e., the second procedure is right). The first process you described (adding 5 mL water 1 mL X), you are actually diluting the solvent 6 times.

Chakchel puts it correctly

"Don't mix dilution and ratio...

Ratio means you have x parts of A and y parts of B.

x : y

Dilution refers to the total volume.

x : (x+y)"

http://www.protocol-online.org/biology-forums-2/posts/15340.html

To avoid confusion concentration is a better parameter.

You may possibly find useful to check my post elsewhere at this forum, for a specific example: https://www.researchgate.net/post/How_do_we_determine_the_actual_amount_of_MnNO32_in_a_45-50_w_w_solution

Dear Tuhin Khan

Yes, it is ratio. So, you ensure that the appropriate procedure is dilute 1 ml of sovent X in 6 ml of H2O. Considering that: 

Ratio means you have x parts of A and y parts of B --->  x : y

If so, thank you a lot, but could you explain me the first one?

Dilution refers to the total volume ---> x : (x+y)"

Does that mean 1 ml of solvent X must be diluted in the total solution (1 ml of solvent X + 5 ml of H2O)? It's like 2 ml of solvent X diluted in 5 ml of H2O.

I am lost now. "It's like 2 ml of solvent X diluted in 5 ml of H2O" Do you mean 2 ml or 1 ml?

1 ml solvent X adding to 5 ml water will dilute solvent X by 6 times (1:(1+5)) similarly it will dilute water by 6/5 times. In this case the solvent ratio is X : water = 1: 5.

Yes, it is 2 ml because:

"x : (x+y)" ---> x (1 ml X) : (x+y ---> 1 ml X + 5 ml H2O).

Is it correct?